Methods and apparatus for joint multi-AP transmission in WLANs

ABSTRACT

A method of multi-access point (multi-AP) communication performed by a wireless transmit/receive unit (WTRU) comprises: receiving ( 1510 ) a first trigger frame from a first access point (AP) of a plurality of APs, the first trigger frame comprising first information; receiving ( 1520 ) a second trigger frame from a second AP of the plurality of APs at a predetermined time duration after receiving the first trigger frame, the second trigger frame also comprising the first information of the first trigger frame; generating ( 1530 ) a synchronization frame based on the first trigger frame and the second trigger frame, the synchronization frame comprising synchronization information; transmitting the synchronization frame to at least the first AP and the second AP; and receiving ( 1540 ) a data transmission based on the synchronization information from each of the first AP and the second AP.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage, under 35 U.S.C. § 371, ofInternational Application No. PCT/US2019/060441 filed Nov. 8, 2019,which claims the benefit of U.S. Provisional Application No. 62/757,611,filed Nov. 8, 2018, and the benefit of U.S. Provisional Application No.62/815,113, filed Mar. 7, 2019, the contents of which are incorporatedherein by reference.

BACKGROUND

A WLAN in Infrastructure Basic Service Set (BSS) mode has an AccessPoint (AP) for the BSS and one or more stations (STAs) associated withthe AP. The AP typically has access or interface to a DistributionSystem (DS) or another type of wired/wireless network that carriestraffic in and out of the BSS. Traffic to STAs that originates fromoutside the BSS arrives through the AP and is delivered to the STAs.Traffic originating from STAs to destinations outside the BSS is sent tothe AP to be delivered to the respective destinations. Traffic betweenSTAs within the BSS may also be sent through the AP where the source STAsends traffic to the AP and the AP delivers the traffic to thedestination STA. Such traffic between STAs within a BSS is reallypeer-to-peer traffic. Such peer-to-peer traffic may also be sentdirectly between the source and destination STAs with a direct linksetup (DLS) using an 802.11e DLS or an 802.11z tunnelled DLS (TDLS). AWLAN using an Independent BSS (IBSS) mode has no AP, and/or STAs,communicating directly with each other. This mode of communication isreferred to as an “ad-hoc” mode of communication.

In downlink coordinated single user (SU) beamforming or joint precoding,methods are needed for the APs to synchronize to the STA such that thesignals may reach the STA with similar received power, time, andfrequency to enable proper decoding of the signal by the STA. Inaddition, channel access schemes that enable this operation need to bedefined.

SUMMARY

A method of multi-access point (multi-AP) communication performed by awireless transmit/receive unit (WTRU) comprises receiving a firsttrigger frame from a first access point (AP) of a plurality of APs, thefirst trigger frame comprising first information. The WTRU receives asecond trigger frame from a second AP of the plurality of APs at apredetermined time duration after receiving the first trigger frame. Thesecond trigger frame also comprises the first information of the firsttrigger frame. The WTRU generates a synchronization frame based on thefirst trigger frame and the second trigger frame. The synchronizationframe comprises synchronization information. The WTRU transmits thesynchronization frame at least the first AP and the second AP. Finally,the WTRU receives a data transmission based on the synchronizationinformation from each of the first AP and the second AP.

A wireless transmit/receive unit (WTRU) configured to perform amulti-access point (multi-AP) communication comprises: a receiverconfigured to receive a first trigger frame from a first access point(AP) of a plurality of APs. The first trigger frame comprises firstinformation. The receiver is also configured to receive a second triggerframe from a second AP of the plurality of APs at a predetermined timeduration after receiving the first trigger frame. The second triggerframe also comprises the first information of the first trigger frame.The WTRU further comprises a processor configured to generate asynchronization frame based on the first trigger frame and the secondtrigger frame. The synchronization frame comprises synchronizationinformation. The WTRU further comprises a transmitter configured totransmit the synchronization frame to at least the first AP and thesecond AP. Further, the receiver is configured to receive a datatransmission based on the synchronization information from each of thefirst AP and the second AP.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawings,wherein like reference numerals in the figures indicate like elements,and wherein:

FIG. 1A is a system diagram illustrating an example communicationssystem in which one or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram illustrating an example wirelesstransmit/receive unit (WTRU) that may be used within the communicationssystem illustrated in FIG. 1A according to an embodiment;

FIG. 10 is a system diagram illustrating an example radio access network(RAN) and an example core network (CN) that may be used within thecommunications system illustrated in FIG. 1A according to an embodiment;

FIG. 1D is a system diagram illustrating a further example RAN and afurther example CN that may be used within the communications systemillustrated in FIG. 1A according to an embodiment;

FIG. 2 illustrates a fractional frequency reuse (FFR) in coordinatedOrthogonal Frequency-Division Multiple Access (OFDMA);

FIG. 3 illustrates an associated OFDMA resource allocation for theexample of FIG. 2 ;

FIG. 4 illustrates example coordinated nulling/beamforming;

FIG. 5 illustrates a single-user joint precoded multi-AP transmission;

FIG. 6 illustrates a multi-user joint precoded Multi-AP transmission;

FIG. 7 illustrates example trigger-based multi-AP sounding;

FIG. 8 illustrates an example uplink (UL) sounding phase offset;

FIG. 9 illustrates an example of coordinated MU beamforming;

FIG. 10 illustrates an example trigger frame based downlink (DL) jointtransmission;

FIG. 11 illustrates an exemplary channel access procedure;

FIG. 12 illustrates an exemplary channel access procedure;

FIG. 13 illustrates an exemplary channel access procedure;

FIG. 14 illustrates an exemplary channel access procedure;

FIG. 15 illustrates an exemplary channel access procedure;

FIG. 16 illustrates an exemplary channel access procedure;

FIG. 17 illustrates an exemplary channel access procedure;

FIG. 18 illustrates an exemplary channel access procedure;

FIG. 19 illustrates an exemplary channel access procedure;

FIG. 20 illustrates an exemplary channel access procedure;

FIG. 21 illustrates an example procedure and frame exchange for anexample JT MU-MIMO;

FIG. 22 illustrates an example procedure and frame exchange for anexample JT MU-MIMO;

FIG. 23 illustrates an example procedure and frame exchange for anexample JT MU-MIMO; and

FIG. 24 illustrates an example procedure and frame exchange for anexample JT MU-MIMO.

DETAILED DESCRIPTION

FIG. 1A is a diagram illustrating an example communications system 100in which one or more disclosed embodiments may be implemented. Thecommunications system 100 may be a multiple access system that providescontent, such as voice, data, video, messaging, broadcast, etc., tomultiple wireless users. The communications system 100 may enablemultiple wireless users to access such content through the sharing ofsystem resources, including wireless bandwidth. For example, thecommunications systems 100 may employ one or more channel accessmethods, such as code division multiple access (CDMA), time divisionmultiple access (TDMA), frequency division multiple access (FDMA),orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tailunique-word discrete Fourier transform Spread OFDM (ZT-UW-DFT-S-OFDM),unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bankmulticarrier (FBMC), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN)104, a core network (CN) 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d, any of which maybe referred to as a station (STA), may be configured to transmit and/orreceive wireless signals and may include a user equipment (UE), a mobilestation, a fixed or mobile subscriber unit, a subscription-based unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watchor other wearable, a head-mounted display (HMD), a vehicle, a drone, amedical device and applications (e.g., remote surgery), an industrialdevice and applications (e.g., a robot and/or other wireless devicesoperating in an industrial and/or an automated processing chaincontexts), a consumer electronics device, a device operating oncommercial and/or industrial wireless networks, and the like. Any of theWTRUs 102 a, 102 b, 102 c and 102 d may be interchangeably referred toas a UE.

The communications systems 100 may also include a base station 114 aand/or a base station 114 b. Each of the base stations 114 a, 114 b maybe any type of device configured to wirelessly interface with at leastone of the WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to oneor more communication networks, such as the CN 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a NodeB, an eNode B(eNB), a Home Node B, a Home eNode B, anext generation NodeB, such as agNodeB (gNB), a new radio (NR) NodeB, a site controller, an access point(AP), a wireless router, and the like. While the base stations 114 a,114 b are each depicted as a single element, it will be appreciated thatthe base stations 114 a, 114 b may include any number of interconnectedbase stations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, and the like. The base station 114 a and/or the base station 114b may be configured to transmit and/or receive wireless signals on oneor more carrier frequencies, which may be referred to as a cell (notshown). These frequencies may be in licensed spectrum, unlicensedspectrum, or a combination of licensed and unlicensed spectrum. A cellmay provide coverage fora wireless service to a specific geographicalarea that may be relatively fixed or that may change over time. The cellmay further be divided into cell sectors. For example, the cellassociated with the base station 114 a may be divided into threesectors. Thus, in one embodiment, the base station 114 a may includethree transceivers, i.e., one for each sector of the cell. In anembodiment, the base station 114 a may employ multiple-input multipleoutput (MIMO) technology and may utilize multiple transceivers for eachsector of the cell. For example, beamforming may be used to transmitand/or receive signals in desired spatial directions.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet(UV), visible light, etc.). The air interface 116 may be establishedusing any suitable radio access technology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink(DL) Packet Access (HSDPA) and/or High-Speed Uplink (UL) Packet Access(HSUPA).

In an embodiment, the base station 114 a and the WTRUs 102 a, 102 b, 102c may implement a radio technology such as Evolved UMTS TerrestrialRadio Access (E-UTRA), which may establish the air interface 116 usingLong Term Evolution (LTE) and/or LTE-Advanced (LTE-A) and/orLTE-Advanced Pro (LTE-A Pro).

In an embodiment, the base station 114 a and the WTRUs 102 a, 102 b, 102c may implement a radio technology such as NR Radio Access, which mayestablish the air interface 116 using NR.

In an embodiment, the base station 114 a and the WTRUs 102 a, 102 b, 102c may implement multiple radio access technologies. For example, thebase station 114 a and the WTRUs 102 a, 102 b, 102 c may implement LTEradio access and NR radio access together, for instance using dualconnectivity (DC) principles. Thus, the air interface utilized by WTRUs102 a, 102 b, 102 c may be characterized by multiple types of radioaccess technologies and/or transmissions sent to/from multiple types ofbase stations (e.g., an eNB and a gNB).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.11 (i.e.,Wireless Fidelity (WiFi), IEEE 802.16 (i.e., Worldwide Interoperabilityfor Microwave Access (WiMAX)), CDMA2000, CDMA2000 1×, CDMA2000 EV-DO,Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), InterimStandard 856 (IS-856), Global System for Mobile communications (GSM),Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and thelike.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, an industrialfacility, an air corridor (e.g., for use by drones), a roadway, and thelike. In one embodiment, the base station 114 b and the WTRUs 102 c, 102d may implement a radio technology such as IEEE 802.11 to establish awireless local area network (WLAN). In an embodiment, the base station114 b and the WTRUs 102 c, 102 d may implement a radio technology suchas IEEE 802.15 to establish a wireless personal area network (WPAN). Inyet another embodiment, the base station 114 b and the WTRUs 102 c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, LTE-A Pro, NR etc.) to establish a picocell or femtocell. Asshown in FIG. 1A, the base station 114 b may have a direct connection tothe Internet 110. Thus, the base station 114 b may not be required toaccess the Internet 110 via the CN 106.

The RAN 104 may be in communication with the CN 106, which may be anytype of network configured to provide voice, data, applications, and/orvoice over internet protocol (VoIP) services to one or more of the WTRUs102 a, 102 b, 102 c, 102 d. The data may have varying quality of service(QoS) requirements, such as differing throughput requirements, latencyrequirements, error tolerance requirements, reliability requirements,data throughput requirements, mobility requirements, and the like. TheCN 106 may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the CN 106 may be in direct or indirectcommunication with other RANs that employ the same RAT as the RAN 104 ora different RAT. For example, in addition to being connected to the RAN104, which may be utilizing a NR radio technology, the CN 106 may alsobe in communication with another RAN (not shown) employing a GSM, UMTS,CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

The CN 106 may also serve as a gateway for the WTRUs 102 a, 102 b, 102c, 102 d to access the PSTN 108, the Internet 110, and/or the othernetworks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) and/orthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired and/or wireless communications networksowned and/or operated by other service providers. For example, thenetworks 112 may include another CN connected to one or more RANs, whichmay employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities (e.g., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks). For example, the WTRU 102 c shown in FIG. 1A may be configuredto communicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram illustrating an example WTRU 102. As shownin FIG. 1B, the WTRU 102 may include a processor 118, a transceiver 120,a transmit/receive element 122, a speaker/microphone 124, a keypad 126,a display/touchpad 128, non-removable memory 130, removable memory 132,a power source 134, a global positioning system (GPS) chipset 136,and/or other peripherals 138, among others. It will be appreciated thatthe WTRU 102 may include any sub-combination of the foregoing elementswhile remaining consistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), anyother type of integrated circuit (IC), a state machine, and the like.The processor 118 may perform signal coding, data processing, powercontrol, input/output processing, and/or any other functionality thatenables the WTRU 102 to operate in a wireless environment. The processor118 may be coupled to the transceiver 120, which may be coupled to thetransmit/receive element 122. While FIG. 1B depicts the processor 118and the transceiver 120 as separate components, it will be appreciatedthat the processor 118 and the transceiver 120 may be integratedtogether in an electronic package or chip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In an embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and/or receive both RF and light signals. It will beappreciated that the transmit/receive element 122 may be configured totransmit and/or receive any combination of wireless signals.

Although the transmit/receive element 122 is depicted in FIG. 1B as asingle element, the WTRU 102 may include any number of transmit/receiveelements 122. More specifically, the WTRU 102 may employ MIMOtechnology. Thus, in one embodiment, the WTRU 102 may include two ormore transmit/receive elements 122 (e.g., multiple antennas) fortransmitting and receiving wireless signals over the air interface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as NR and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs and/or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, a Virtual Reality and/or Augmented Reality (VR/AR) device, anactivity tracker, and the like. The peripherals 138 may include one ormore sensors. The sensors may be one or more of a gyroscope, anaccelerometer, a hall effect sensor, a magnetometer, an orientationsensor, a proximity sensor, a temperature sensor, a time sensor; ageolocation sensor, an altimeter, a light sensor, a touch sensor, amagnetometer, a barometer, a gesture sensor, a biometric sensor, ahumidity sensor and the like.

The WTRU 102 may include a full duplex radio for which transmission andreception of some or all of the signals (e.g., associated withparticular subframes for both the UL (e.g., for transmission) and DL(e.g., for reception) may be concurrent and/or simultaneous. The fullduplex radio may include an interference management unit to reduce andor substantially eliminate self-interference via either hardware (e.g.,a choke) or signal processing via a processor (e.g., a separateprocessor (not shown) or via processor 118). In an embodiment, the WTRU102 may include a half-duplex radio for which transmission and receptionof some or all of the signals (e.g., associated with particularsubframes for either the UL (e.g., for transmission) or the DL (e.g.,for reception)).

FIG. 10 is a system diagram illustrating the RAN 104 and the CN 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the CN 106.

The RAN 104 may include eNode-Bs 160 a, 160 b, 160 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 160 a, 160 b, 160c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 160 a, 160 b, 160 c may implement MIMO technology. Thus,the eNode-B 160 a, for example, may use multiple antennas to transmitwireless signals to, and/or receive wireless signals from, the WTRU 102a.

Each of the eNode-Bs 160 a, 160 b, 160 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the UL and/or DL, and the like. As shown in FIG. 10 , the eNode-Bs160 a, 160 b, 160 c may communicate with one another over an X2interface.

The CN 106 shown in FIG. 10 may include a mobility management entity(MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN)gateway (PGW) 166. While the foregoing elements are depicted as part ofthe CN 106, it will be appreciated that any of these elements may beowned and/or operated by an entity other than the CN operator.

The MME 162 may be connected to each of the eNode-Bs 162 a, 162 b, 162 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 162 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 162 may provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM and/or WCDMA.

The SGW 164 may be connected to each of the eNode Bs 160 a, 160 b, 160 cin the RAN 104 via the S1 interface. The SGW 164 may generally route andforward user data packets to/from the WTRUs 102 a, 102 b, 102 c. The SGW164 may perform other functions, such as anchoring user planes duringinter-eNode B handovers, triggering paging when DL data is available forthe WTRUs 102 a, 102 b, 102 c, managing and storing contexts of theWTRUs 102 a, 102 b, 102 c, and the like.

The SGW 164 may be connected to the PGW 166, which may provide the WTRUs102 a, 102 b, 102 c with access to packet-switched networks, such as theInternet 110, to facilitate communications between the WTRUs 102 a, 102b, 102 c and IP-enabled devices.

The CN 106 may facilitate communications with other networks. Forexample, the CN 106 may provide the WTRUs 102 a, 102 b, 102 c withaccess to circuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. For example, the CN 106 may include,or may communicate with, an IP gateway (e.g., an IP multimedia subsystem(IMS) server) that serves as an interface between the CN 106 and thePSTN 108. In addition, the CN 106 may provide the WTRUs 102 a, 102 b,102 c with access to the other networks 112, which may include otherwired and/or wireless networks that are owned and/or operated by otherservice providers.

Although the WTRU is described in FIGS. 1A-1D as a wireless terminal, itis contemplated that in certain representative embodiments that such aterminal may use (e.g., temporarily or permanently) wired communicationinterfaces with the communication network.

In representative embodiments, the other network 112 may be a WLAN.

A WLAN in Infrastructure Basic Service Set (BSS) mode may have an AccessPoint (AP) for the BSS and one or more stations (STAs) associated withthe AP. The AP may have access or an interface to a Distribution System(DS) or another type of wired/wireless network that carries traffic into and/or out of the BSS. Traffic to STAs that originates from outsidethe BSS may arrive through the AP and may be delivered to the STAs.Traffic originating from STAs to destinations outside the BSS may besent to the AP to be delivered to respective destinations. Trafficbetween STAs within the BSS may be sent through the AP, for example,where the source STA may send traffic to the AP and the AP may deliverthe traffic to the destination STA. The traffic between STAs within aBSS may be considered and/or referred to as peer-to-peer traffic. Thepeer-to-peer traffic may be sent between (e.g., directly between) thesource and destination STAs with a direct link setup (DLS), In certainrepresentative embodiments, the DLS may use an 802.11e DLS or an 802.11ztunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may nothave an AP, and the STAs (e.g., all of the STAs) within or using theIBSS may communicate directly with each other. The IBSS mode ofcommunication may sometimes be referred to herein as an “ad-hoc” mode ofcommunication.

When using the 802.11ac infrastructure mode of operation or a similarmode of operations, the AP may transmit a beacon on a fixed channel,such as a primary channel. The primary channel may be a fixed width(e.g., 20 MHz wide bandwidth) or a dynamically set width. The primarychannel may be the operating channel of the BSS and may be used by theSTAs to establish a connection with the AP. In certain representativeembodiments, Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) may be implemented, for example in 802.11 systems. ForCSMA/CA, the STAs (e.g., every STA), including the AP, may sense theprimary channel. If the primary channel is sensed/detected and/ordetermined to be busy by a particular STA, the particular STA may backoff. One STA (e.g., only one station) may transmit at any given time ina given BSS.

High Throughput (HT) STAs may use a 40 MHz wide channel forcommunication, for example, via a combination of the primary 20 MHzchannel with an adjacent or nonadjacent 20 MHz channel to form a 40 MHzwide channel.

Very High Throughput (VHT) STAs may support 20 MHz, 40 MHz, 80 MHz,and/or 160 MHz wide channels. The 40 MHz, and/or 80 MHz, channels may beformed by combining contiguous 20 MHz channels. A 160 MHz channel may beformed by combining 8 contiguous 20 MHz channels, or by combining twonon-contiguous 80 MHz channels, which may be referred to as an 80+80configuration. For the 80+80 configuration, the data, after channelencoding, may be passed through a segment parser that may divide thedata into two streams. Inverse Fast Fourier Transform (IFFT) processing,and time domain processing, may be done on each stream separately. Thestreams may be mapped on to the two 80 MHz channels, and the data may betransmitted by a transmitting STA. At the receiver of the receiving STA,the above described operation for the 80+80 configuration may bereversed, and the combined data may be sent to the Medium Access Control(MAC).

Sub 1 GHz modes of operation are supported by 802.11af and 802.11ah. Thechannel operating bandwidths, and carriers, are reduced in 802.11af and802.11ah relative to those used in 802.11n, and 802.11ac. 802.11afsupports 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space(TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and16 MHz bandwidths using non-TVWS spectrum. According to a representativeembodiment, 802.11ah may support Meter Type Control/Machine-TypeCommunications (MTC), such as MTC devices in a macro coverage area. MTCdevices may have certain capabilities, for example, limited capabilitiesincluding support for (e.g., only support for) certain and/or limitedbandwidths. The MTC devices may include a battery with a battery lifeabove a threshold (e.g., to maintain a very long battery life).

WLAN systems, which may support multiple channels, and channelbandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include achannel which may be designated as the primary channel. The primarychannel may have a bandwidth equal to the largest common operatingbandwidth supported by all STAs in the BSS. The bandwidth of the primarychannel may be set and/or limited by a STA, from among all STAs inoperating in a BSS, which supports the smallest bandwidth operatingmode. In the example of 802.11ah, the primary channel may be 1 MHz widefor STAs (e.g., MTC type devices) that support (e.g., only support) a 1MHz mode, even if the AP, and other STAs in the BSS support 2 MHz, 4MHz, 8 MHz, 16 MHz, and/or other channel bandwidth operating modes.Carrier sensing and/or Network Allocation Vector (NAV) settings maydepend on the status of the primary channel. If the primary channel isbusy, for example, due to a STA (which supports only a 1 MHz operatingmode) transmitting to the AP, all available frequency bands may beconsidered busy even though a majority of the available frequency bandsremains idle.

In the United States, the available frequency bands, which may be usedby 802.11ah, are from 902 MHz to 928 MHz. In Korea, the availablefrequency bands are from 917.5 MHz to 923.5 MHz. In Japan, the availablefrequency bands are from 916.5 MHz to 927.5 MHz. The total bandwidthavailable for 802.11ah is 6 MHz to 26 MHz depending on the country code.

FIG. 1D is a system diagram illustrating the RAN 104 and the CN 106according to an embodiment. As noted above, the RAN 104 may employ an NRradio technology to communicate with the WTRUs 102 a, 102 b, 102 c overthe air interface 116. The RAN 104 may also be in communication with theCN 106.

The RAN 104 may include gNBs 180 a, 180 b, 180 c, though it will beappreciated that the RAN 104 may include any number of gNBs whileremaining consistent with an embodiment. The gNBs 180 a, 180 b, 180 cmay each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the gNBs 180 a, 180 b, 180 c may implement MIMO technology. For example,gNBs 180 a, 108 b may utilize beamforming to transmit signals to and/orreceive signals from the gNBs 180 a, 180 b, 180 c. Thus, the gNB 180 a,for example, may use multiple antennas to transmit wireless signals to,and/or receive wireless signals from, the WTRU 102 a. In an embodiment,the gNBs 180 a, 180 b, 180 c may implement carrier aggregationtechnology. For example, the gNB 180 a may transmit multiple componentcarriers to the WTRU 102 a (not shown). A subset of these componentcarriers may be on unlicensed spectrum while the remaining componentcarriers may be on licensed spectrum. In an embodiment, the gNBs 180 a,180 b, 180 c may implement Coordinated Multi-Point (CoMP) technology.For example, WTRU 102 a may receive coordinated transmissions from gNB180 a and gNB 180 b (and/or gNB 180 c).

The WTRUs 102 a, 102 b, 102 c may communicate with gNBs 180 a, 180 b,180 c using transmissions associated with a scalable numerology. Forexample, the OFDM symbol spacing and/or OFDM subcarrier spacing may varyfor different transmissions, different cells, and/or different portionsof the wireless transmission spectrum. The WTRUs 102 a, 102 b, 102 c maycommunicate with gNBs 180 a, 180 b, 180 c using subframe or transmissiontime intervals (TTIs) of various or scalable lengths (e.g., containing avarying number of OFDM symbols and/or lasting varying lengths ofabsolute time).

The gNBs 180 a, 180 b, 180 c may be configured to communicate with theWTRUs 102 a, 102 b, 102 c in a standalone configuration and/or anon-standalone configuration. In the standalone configuration, WTRUs 102a, 102 b, 102 c may communicate with gNBs 180 a, 180 b, 180 c withoutalso accessing other RANs (e.g., such as eNode-Bs 160 a, 160 b, 160 c).In the standalone configuration, WTRUs 102 a, 102 b, 102 c may utilizeone or more of gNBs 180 a, 180 b, 180 c as a mobility anchor point. Inthe standalone configuration, WTRUs 102 a, 102 b, 102 c may communicatewith gNBs 180 a, 180 b, 180 c using signals in an unlicensed band. In anon-standalone configuration WTRUs 102 a, 102 b, 102 c may communicatewith/connect to gNBs 180 a, 180 b, 180 c while also communicatingwith/connecting to another RAN such as eNode-Bs 160 a, 160 b, 160 c. Forexample, WTRUs 102 a, 102 b, 102 c may implement DC principles tocommunicate with one or more gNBs 180 a, 180 b, 180 c and one or moreeNode-Bs 160 a, 160 b, 160 c substantially simultaneously. In thenon-standalone configuration, eNode-Bs 160 a, 160 b, 160 c may serve asa mobility anchor for WTRUs 102 a, 102 b, 102 c and gNBs 180 a, 180 b,180 c may provide additional coverage and/or throughput for servicingWTRUs 102 a, 102 b, 102 c.

Each of the gNBs 180 a, 180 b, 180 c may be associated with a particularcell (not shown) and may be configured to handle radio resourcemanagement decisions, handover decisions, scheduling of users in the ULand/or DL, support of network slicing, DC, interworking between NR andE-UTRA, routing of user plane data towards User Plane Function (UPF) 184a, 184 b, routing of control plane information towards Access andMobility Management Function (AMF) 182 a, 182 b and the like. As shownin FIG. 1D, the gNBs, 180 a, 180 b, 180 c may communicate with oneanother over an Xn interface.

The CN 106 shown in FIG. 1D may include at least one AMF 182 a, 182 b,at least one UPF 184 a, 184 b, at least one Session Management Function(SMF) 183 a, 183 b, and possibly a Data Network (DN) 185 a, 185 b. Whilethe foregoing elements are depicted as part of the CN 106, it will beappreciated that any of these elements may be owned and/or operated byan entity other than the CN operator.

The AMF 182 a, 182 b may be connected to one or more of the gNBs 180 a,180 b, 180 c in the RAN 104 via an N2 interface and may serve as acontrol node. For example, the AMF 182 a, 182 b may be responsible forauthenticating users of the WTRUs 102 a, 102 b, 102 c, support fornetwork slicing (e.g., handling of different protocol data unit (PDU)sessions with different requirements), selecting a particular SMF 183 a,183 b, management of the registration area, termination of non-accessstratum (NAS) signaling, mobility management, and the like. Networkslicing may be used by the AMF 182 a, 182 b in order to customize CNsupport for WTRUs 102 a, 102 b, 102 c based on the types of servicesbeing utilized WTRUs 102 a, 102 b, 102 c. For example, different networkslices may be established for different use cases such as servicesrelying on ultra-reliable low latency (URLLC) access, services relyingon enhanced massive mobile broadband (eMBB) access, services for MTCaccess, and the like. The AMF 182 a, 182 b may provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro,and/or non-3GPP access technologies such as WiFi.

The SMF 183 a, 183 b may be connected to an AMF 182 a, 182 b in the CN106 via an N11 interface. The SMF 183 a, 183 b may also be connected toa UPF 184 a, 184 b in the CN 106 via an N4 interface. The SMF 183 a, 183b may select and control the UPF 184 a, 184 b and configure the routingof traffic through the UPF 184 a, 184 b. The SMF 183 a, 183 b mayperform other functions, such as managing and allocating UE IP address,managing PDU sessions, controlling policy enforcement and QoS, providingDL data notifications, and the like. A PDU session type may be IP-based,non-IP based, Ethernet-based, and the like.

The UPF 184 a, 184 b may be connected to one or more of the gNBs 180 a,180 b, 180 c in the RAN 104 via an N3 interface, which may provide theWTRUs 102 a, 102 b, 102 c with access to packet-switched networks, suchas the Internet 110, to facilitate communications between the WTRUs 102a, 102 b, 102 c and IP-enabled devices. The UPF 184, 184 b may performother functions, such as routing and forwarding packets, enforcing userplane policies, supporting multi-homed PDU sessions, handling user planeQoS, buffering DL packets, providing mobility anchoring, and the like.

The CN 106 may facilitate communications with other networks. Forexample, the CN 106 may include, or may communicate with, an IP gateway(e.g., an IP multimedia subsystem (IMS) server) that serves as aninterface between the CN 106 and the PSTN 108. In addition, the CN 106may provide the WTRUs 102 a, 102 b, 102 c with access to the othernetworks 112, which may include other wired and/or wireless networksthat are owned and/or operated by other service providers. In oneembodiment, the WTRUs 102 a, 102 b, 102 c may be connected to a local DN185 a, 185 b through the UPF 184 a, 184 b via the N3 interface to theUPF 184 a, 184 b and an N6 interface between the UPF 184 a, 184 b andthe DN 185 a, 185 b.

In view of FIGS. 1A-1D, and the corresponding description of FIGS.1A-1D, one or more, or all, of the functions described herein withregard to one or more of: WTRU 102 a-d, Base Station 114 a-b, eNode-B160 a-c, MME 162, SGW 164, PGW 166, gNB 180 a-c, AMF 182 a-b, UPF 184a-b, SMF 183 a-b, DN 185 a-b, and/or any other device(s) describedherein, may be performed by one or more emulation devices (not shown).The emulation devices may be one or more devices configured to emulateone or more, or all, of the functions described herein. For example, theemulation devices may be used to test other devices and/or to simulatenetwork and/or WTRU functions.

The emulation devices may be designed to implement one or more tests ofother devices in a lab environment and/or in an operator networkenvironment. For example, the one or more emulation devices may performthe one or more, or all, functions while being fully or partiallyimplemented and/or deployed as part of a wired and/or wirelesscommunication network in order to test other devices within thecommunication network. The one or more emulation devices may perform theone or more, or all, functions while being temporarilyimplemented/deployed as part of a wired and/or wireless communicationnetwork. The emulation device may be directly coupled to another devicefor purposes of testing and/or performing testing using over-the-airwireless communications.

The one or more emulation devices may perform the one or more, includingall, functions while not being implemented/deployed as part of a wiredand/or wireless communication network. For example, the emulationdevices may be utilized in a testing scenario in a testing laboratoryand/or a non-deployed (e.g., testing) wired and/or wirelesscommunication network in order to implement testing of one or morecomponents. The one or more emulation devices may be test equipment.Direct RF coupling and/or wireless communications via RF circuitry(e.g., which may include one or more antennas) may be used by theemulation devices to transmit and/or receive data.

A wireless local area network (WLAN) in Infrastructure Basic Service Set(BSS) mode can have an Access Point (AP) for the BSS and one or morestations (STAs) associated with the AP. The AP typically has access orinterface to a Distribution System (DS) or another type ofwired/wireless network that carries traffic in and out of the BSS.Traffic to STAs that originates from outside the BSS arrives through theAP and is delivered to the STAs. Traffic originating from STAs todestinations outside the BSS is sent to the AP to be delivered to therespective destinations. Traffic between STAs within the BSS may also besent through the AP where the source STA sends traffic to the AP and theAP delivers the traffic to the destination STA. Such traffic betweenSTAs within a BSS can be referred to as peer-to-peer traffic. Suchpeer-to-peer traffic may also be sent directly between the source anddestination STAs with a direct link setup (DLS) using an 802.11e DLS oran 802.11z tunnelled DLS (TDLS). A WLAN in Independent BSS (IBSS) modehas no AP, and STAs, communicate directly with each other. This mode ofcommunication can be referred to as an “ad-hoc” mode of communication.

In some implementations, e.g., systems using the infrastructure mode ofoperation specified in the Institute of Electrical and ElectronicsEngineers (IEEE) 802.11ac standard, an AP may transmit a beacon on afixed channel, usually the primary channel. This channel may be 20 MHzwide, and is the operating channel of the BSS. This channel may also beused by STAs to establish a connection with the AP. Channel access in an802.11 systems is implemented using Carrier Sense Multiple Access withCollision Avoidance (CSMA/CA). In this mode of operation, every STA,including the AP, can sense the primary channel. If the channel isdetected to be busy, the STA backs off. Hence only one STA may transmitat any given time in a given BSS.

In some implementations, e.g., systems complying with the IEEE 802.11nstandard, High Throughput (HT) STAs may also use a 40 MHz wide channelfor communication. This can be achieved by combining the primary 20 MHzchannel, with an adjacent 20 MHz channel to form a 40 MHz widecontiguous channel.

In some implementations, e.g., systems complying with the IEEE 802.11acstandard, Very High Throughput (VHT) STAs may support 20 MHz, 40 MHz, 80MHz, and 160 MHz wide channels. The 40 MHz, and 80 MHz, channels may beformed by combining contiguous 20 MHz channels similar to 802.11ndescribed above. A160 MHz channel may be formed either by combining 8contiguous 20 MHz channels, or by combining two non-contiguous 80 MHzchannels, which may be referred to as an 80+80 configuration. For an80+80 configuration, the data, after channel encoding, may be passedthrough a segment parser that divides it into two streams. IFFT, andtime domain, processing may be performed on each stream separately. Thestreams may then be mapped onto the two channels, and the data may betransmitted. At the receiver, this mechanism is reversed, and thecombined data is sent to the MAC.

In some implementations, e.g., systems complying with IEEE 802.11af,and/or IEEE 802.11ah standards, Sub 1 GHz modes of operation aresupported. In such implementations, the channel operating bandwidths,and carriers, may be reduced relative to those used in systems complyingwith the IEEE 802.11n and/or IEEE 802.11ac standards. For example,802.11af supports 5 MHz, 10 MHz and 20 MHz bandwidths in the TV WhiteSpace (TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz,and 16 MHz bandwidths using non-TVWS spectrum. A possible use case for802.11ah is support for Meter Type Control or Machine TypeCommunications (MTC) devices in a macro coverage area. MTC devices mayhave limited capabilities such as support for limited bandwidths, andmay include a requirement for a very long battery life.

WLAN systems which support multiple channels and/or channel widths, suchas those complying with IEEE 802.11n, 802.11ac, 802.11af, and/or802.11ah standards, may include a channel which is designated as theprimary channel. The primary channel may, but not necessarily, have abandwidth equal to the largest common operating bandwidth supported byall STAs in the BSS. In such cases the bandwidth of the primary channelmay therefore be limited by the STA, of all STAs in operating in a BSS,which supports the smallest bandwidth operating mode. In the example ofIEEE 802.11ah systems, the primary channel may be 1 MHz wide if the BSSincludes STAs (e.g., MTC type devices) that only support a 1 MHz modeeven if the AP, and other STAs in the BSS, may support a 2 MHz, 4 MHz, 8MHz, 16 MHz, or other channel bandwidth operating modes. Carrier sensingand NAV settings may depend on the status of the primary channel. Insome such cases, if the primary channel is busy, e.g., due to a STAsupporting only a 1 MHz operating mode is transmitting to the AP, thenthe entire available frequency bands are considered busy even thoughmajority of it stays idle and available.

In the United States, the available frequency bands which may be used by802.11ah compliant systems are from 902 MHz to 928 MHz. In Korea it isfrom 917.5 MHz to 923.5 MHz; and in Japan, it is from 916.5 MHz to 927.5MHz. The total bandwidth available for 802.11ah is 6 MHz to 26 MHzdepending on the country code.

Recently, the IEEE 802.11 High Efficiency WLAN (HEW) Study Group (SG)was created to explore the scope and purpose of a possible, futureamendment to enhance the quality of service all users experience for abroad spectrum of wireless users in many usage scenarios includinghigh-density scenarios in the 2.4 GHz, 5 GHz and 6 GHz band. New usecases which support dense deployments of APs, and STAs, and associatedRadio Resource Management (RRM) technologies are being considered by theHEW SG.

In a typical 802.11 network (i.e., a network complying with one or moreIEEE 802.11 standards), STAs are associated with a single AP and cantransmit to and from that AP with little or no coordination withtransmissions in neighboring BSSs. A STA may defer to an overlapping BSS(OBSS) transmission based on a CSMA protocol that is entirelyindependent between BSSs. In some systems (e.g., 802.11ax compliantsystems), some level of coordination between OBSSs can be implementedusing spatial re-use procedures to allow OBSS transmissions based on anadjusted energy detection threshold (e.g., using an OBSS packetdetection (OBSS PD) procedure) or by knowledge of the amount ofinterference that could be tolerated by a receiving OBSS STA (e.g.,using a spatial reuse parameter (SRP) procedure).

Some implementations include procedures to allow for more coordinationbetween the OBSSs by allowing transmission to or from multiple APs to asingle or multiple STAs. In some implementations, this is similar toCoordinated Multi-point (CoMP) transmission in systems complying with3GPP LTE Release 10, but in some implementations, such procedures workwithin an unlicensed band and/or are specific to one or more IEEE 802.11protocols.

In systems supporting Coordinated multi-point (CoMP) transmission,multiple eNBs (or other types of base stations—eNB is used forconvenience) may transmit to the same or multiple WTRUs in the same timeand frequency resource using joint processing/transmission. This canhave the effect of improving overall throughput for the considered WTRU.Dynamic cell selection may be treated as a special case of jointprocessing in which only one of the set of WTRUs is activelytransmitting data at any time. On the other hand, multiple eNBs maytransmit to different WTRUs (each eNB serving its own WTRU) in the sametime and frequency resource using coordinated beamforming/scheduling.This can have the effect of reducing interference experienced by eachWTRU. Significant improvements of cell average and/or cell edgethroughput may be achieved using CoMP, e.g., in LTE systems. In someimplementations, multiple transmit antennas are assumed available foreach base station. Simultaneous interference suppression (for otherWTRUss) and signal quality optimization (for the desired WTRU) may beperformed using spatial domain signal processing at each base station.

In some implementations, some degree of channel state information isassumed available at the base stations, e.g., through explicit feedback.Further, in some implementations, some degree of timing/frequencysynchronization is assumed, e.g., to avoid more complicated signalprocessing to deal with inter-carrier interference (or inter-symbolinterference). Further, in some implementations, the level ofcoordination between the eNBs may affect the specific CoMP scheme thatmay be possible.

Multi-AP transmission schemes in WLANs may be referred to using severalclassifications, including Coordinated OFDMA, CoordinatedNulling/Beamforming, and Coordinated SU/MU Transmission.

In coordinated OFDMA, each group of RUs may be used by one AP only totransmit or receive data. The information may be beamformed or mayinclude MU-MIMO on each RU. Complexity can be described as relativelylow to moderate. In some simple coordinated OFDMA schemes, the APs maydivide the OFDMA RUs among themselves in a coordinated manner, with eachAP restricted to specific RUs. In some more sophisticated coordinatedOFDMA scheme, the APs allow STAs that are not affected by interferenceor will not affect others to utilize the entire bandwidth whilerestricting access for the STAs that may be affected. This approach maybe referred to as fractional frequency reuse (FFR).

FIG. 2 illustrates FFR in coordinated OFDMA. The center group may useall the channels where the edge groups may use different channels.

FIG. 3 illustrates an associated OFDMA resource allocation for theexample of FIG. 2 . In this example, group 1 may use both subband 1 andsubband 2. Group 2 may use subband 1 and Group 3 may use subband 2. InCoordinated Nulling/Beamforming (CN/CB), each AP may apply precoding totransmit information to or from its desired STA(s) and may suppressinterference to or from other STA(s).

FIG. 4 illustrates example CN/CB. As shown in FIG. 4 , there are an AP2and a STA1. A data transmission between the AP1 and the STA1 is adesired data transmission 410. There are also an AP2 and a STA1. A datatransmission between the AP2 and the STA2 is a desired data transmission420. However, in this scenario, the AP1 might also transmit data toanother STA or other STAs, and thus there may be an interference datatransmission, i.e., an interference 430. The AP2 might also transmitdata to another STA or other STAs, and thus there may be an interferencedata transmission, i.e., an interference 440. In some such cases, thedata for each STA is only needed at its associated AP although channelinformation from the other STA may be needed at both APs.

In coordinated single user (SU) or multi user (MU) transmission,multiple APs may coordinate to transmit information to or from a singleSTA or multiple GSTAs simultaneously. In some such cases, both thechannel information and the data for the STA(s) are needed at both APs.It may be a Coordinated SU Transmission.

In the Coordinated SU Transmission: multiple APs transmit to a STA inone RU. The Coordinated SU transmission may include, in order ofincreased complexity, either Dynamic Point Selection, Coordinated SUBeamforming or Joint Precoding.

FIG. 5 illustrates single-user joint precoded multi-AP transmission orcoordinated SU beamforming. As shown in FIG. 5 , in Dynamic PointSelection, the transmission may be dynamically selected from one of theset of APs. In some such implementations, this selection may incorporateHARQ. In Coordinated SU Beamforming or Joint Precoding, the transmissionmay be from the plurality of APs simultaneously, and the transmissionmay be beamformed or precoded to the desired STA on one or more RUs. Asshown in FIG. 5 , both AP1 and AP2 may do transmission to a STA, i.e.,STA1.

FIG. 6 illustrates a multi-user joint precoded Multi-AP transmission orCoordinated MU Beamforming. In Coordinated MU Beamforming, multiple APstransmit or receive data to/from multiple STAs on one or more RUs. Asshown in FIG. 6 , there are two APs (i.e., AP1 and AP2) and two STAs(i.e., STA1 and STA2). AP1 may transmit data to STA1, and AP2 maytransmit data to STA2. Meanwhile, AP1 may also transmit data to a STAother than STA1, and AP2 may also transmit data to a STA other thanSTA2. Further, there may be a wireless backhaul in which a trigger frame(TF) is sent from AP1 to AP2.

Various techniques discussed herein relate to Joint Multi-APTransmission. Various Multi-AP schemes may be considered for EHTapplications, including coordinated beamforming and joint processing.

Some implementations address synchronization between multiple APs forthe phase calculation in UL sounding/channel estimation. For DL MIMOchannel estimation with increasingly large numbers of antennas, theamount of feedback and quantization errors may make DL soundingundesirable. Assuming channel reciprocity, in some implementations, anUL sounding can be used to replace DL sounding for the purpose of DLMIMO transmission. In some implementations, for UL sounding to a singleAP, no feedback is needed from a non-AP STA. In some implementations,for UL sounding to multiple APs, only feedback of a partial channel(channel observed at a slave AP) is needed.

In a DL sounding procedure, in some implementations, a non-AP STA is theentity measuring the signal and/or estimating the channel. The non-APSTA in this case has perfect knowledge of received signal phasedifferences between Rx antennas at the non-AP STA. However, in ULsounding with multiple APs, APs do not have a common reference clock.When estimated channels from multiple APs are combined, the phasedifference between channels measured by different APs are not known insome implementations.

In the following example, which illustrates the multi-AP UL soundingproblem, the following are assumed: (1) the master AP performs its ownchannel estimation and the slave APs' channel estimations; (2) themaster AP performs precoder calculations and informs the precodercorresponding to slave AP's antennas, using a frame (referred to asframe A) such as a trigger frame (TF); (3) an inter-frame spacing (IFS)after transmitting frame A, the master AP begins joint transmission; (4)an IFS after receiving frame A, the slave AP begins joint transmission.

FIG. 7 illustrates example trigger-based multi-AP sounding. In FIG. 7 ,a master AP (i.e., AP1) will transmit data to a WTRU 710. AP1 mayinitiate UL sounding by sending a null data packet (NDP) Announcement(NDP-A) and trigger frame (TF) for UL sounding. After receiving the TF,a slave AP (i.e., AP2 or a non-AP STA) adjusts its oscillator such thatcarrier frequency offset (CFO) and/or sampling frequency offset (SFO)are corrected relative to AP1. Although the oscillator frequency isaligned, AP2 still does not know the clock at AP1 corresponding to itsown clock in this example.

FIG. 8 illustrates an example UL sounding phase offset. As shown in FIG.8 , a WTRU 810 transmits UL sounding signal to AP1 and AP2. Then, thesounding signal is received at AP2. AP2 is able to estimate the channelamplitude and phases between its own antennas and the transmittingnon-AP STA. Assuming a wireless backhaul in which a TF is sent from AP1to AP2, the channel observed at AP2 can then be reported back to AP1.However, in some implementations AP1 would not be able to combine thisinformation with its own channel estimation because it has performedchannel estimation at a time that is potentially slightly different,which may result in a phase offset between AP1 and AP2's estimatedchannels.

In some implementations, to avoid this phase offset problem, the AP1would need information regarding the time that AP2 performed channelestimation with respect to APIs clock. In some implementations, thiswould require clock synchronization between the master and slave AP inaddition to CFO/SFO correction. It may be desired to provide systems andmethods where no clock synchronization is needed between master/slaveAPs for the purpose of channel estimation and joint DL transmission.

Some implementations address Downlink Coordinated SU Beamforming orJoint Precoding. In downlink Coordinated SU Beamforming or JointPrecoding, it may be desired to provide methods, systems, and devicesfor the APs to synchronize to a STA such that the signals reach the STAwith similar received powers, times and frequencies, e.g., to enableproper decoding of the signal by the STA. Further, it may be desired todefine corresponding channel access schemes.

Some implementations address Uplink Coordinated SU Beamforming or JointPrecoding. In some implementations, transmission from a single STA to asingle AP is supported. In uplink Coordinated SU Beamforming or JointPrecoding or dynamic AP selection, it may be desired to provide channelaccess methods for the STA to send signals to one or more APs.

Some implementations address Coordinated MU beamforming. In coordinatedMU beamforming, several example scenarios may occur.

In a first example, APs may have vastly differentimpairments/configurations. For example, the APs may have differenttransmit powers and/or error vector magnitudes (EVM). In such cases, itmay be desired to balance the transmit powers, e.g., to enable inversionof the effective channel for MU-transmission. In a case where the APshave different transmit powers to the STAs, the resulting effectivechannel may not be invertible (e.g., the effective channel may have ahigh condition number).

FIG. 9 illustrates an example of coordinated MU beamforming. In thisexample, the received signal at each STA {y1, y2} may be modeled as:

$\begin{bmatrix}{y1} \\{y2}\end{bmatrix} = {{{\begin{bmatrix}{h11} & {h12} \\{h21} & {h22}\end{bmatrix}\begin{bmatrix}a & b \\c & d\end{bmatrix}}\begin{bmatrix}e & 0 \\0 & f\end{bmatrix}}\begin{bmatrix}{x\; 1} \\{x2}\end{bmatrix}}$

where [y1 y2]′ are the received signals, h_{i,j} are the effectivechannels from APi to STA j, [a b; c d] is the precoding matrix, [e, 0;0; f] represents any baseband scaling done at the AP and x1 and x2 arethe transmitted signals to STA 1 and STA 2 respectively.

In cases where the APs have different transmit powers to the STAs, theeffective channel may be modeled as:

$\begin{bmatrix}{h11} & {h12} \\{h21} & {h22}\end{bmatrix} = {\begin{bmatrix}{v} & {w} \\{v} & {w}\end{bmatrix} = {\begin{bmatrix} & \\ & \end{bmatrix}\begin{bmatrix}v & 0 \\0 & w\end{bmatrix}}}$

where v and w are the effect of each APs power on the effective channel.To invert the channel for a ZF precoder, the effective channel may beinverted as:

${{inv}( \begin{bmatrix}{h11} & {h12} \\{h21} & {h22}\end{bmatrix} )} = {{{inv}( \begin{bmatrix}v & 0 \\0 & w\end{bmatrix} )}{{inv}( \begin{bmatrix} & \\ & \end{bmatrix} )}}$

If there is a large power imbalance in the APs (e.g., v>>w), then theresulting channel may have a high condition number and inverting thechannel may be problematic.

Some implementations provide UL sounding and channel estimation frommultiple APs without clock synchronization. Such examples may addressissues relating to synchronization between multiple APs for phasecalculation in UL sounding and/or channel estimation.

FIG. 10 illustrates example trigger frame based DL joint transmissionbased on the steps discussed above. As shown in FIG. 10 , AP1 transmitsa trigger frame (TF) to AP2, and AP1 and AP2 transmit data to a WTRU1010 respectively. In this example, the DL signal from AP1 arrives(x+y)−z before the DL signal from AP2, at the non-AP STA. Here, x,y,zcorresponds to the propagation delays in each of the signals in FIG. 10.

In some implementations, the master AP does not need to know x, y and zindividually to combine the channel estimated by itself and slave Aps;rather, in such implementations the master AP needs only to know thevalue of Δt=(x+y)−z.

For example, in some implementations the AP can combine the channelestimations as follows:H=[H _(AP1) e ^(2πfΔt) H _(AP2)],or,H=[H _(AP1) H _(AP2) e ^(−2πfΔt)],

where H_(AP1) and H_(AP2) correspond to the estimated channels at AP1and AP2. In this case, the master AP can the use H to perform precoding.

Alternatively, in some implementations the master AP can use:H=[H _(AP1) H _(AP2)].

as the combined channel to calculate a precoder. However, in this casethe AP1 can delay its DL joint transmission (e.g., until IFS+Δt aftertransmitting TF, or until it instructs slave AP to advance itstransmission, e.g., IFS−Δt after receiving TF). Such delay adjustmentsmay be dependent on subcarrier frequencies.

In some implementations, Δt can be acquired by the master AP based onthe time difference between the time the master AP receives thestart/end of a frame B, (e.g., a sounding feedback, or other frame fromslave AP), and when the master AP receives the start and/or end of theUL sounding signal from the non-AP STA, minus a fixed delay D, where Dis a known delay between the time the slave AP receives the start of ULsignal, and the time the slave AP starts to transmit frame B. Someadjustments can also be made to frame length difference between frame Band the sounding signal, e.g., if the end of the frame is used tocalculate the difference.

FIG. 11 illustrates this UL sounding scenario. As shown in FIG. 11 , aWTRU 1110 may transmit a UL sound signal to AP1 and AP2 respectively.AP1 may observes Δt=z−(x+y) by calculating the time between rx ULsounding, and rx UL sounding feedback, minus a fixed delay D. AP2transmits UL sound feedback to AP1, with a fixed delay D after rx ULsounding signal.

If multiple non-AP STAs perform UL sounding simultaneously, this examplescenario can be applied using one STA and one AP1/AP2 antenna pair as areference, such that the Δt is calculated using this reference antennapairs. Although different STAs may have different Δt, the phasedifference between H_(AP1) and H_(AP2) may be adjusted automaticallye.g., because the same entity (AP1 or AP2) was observing/estimatingmultiple STAs.

In some implementations, if multiple non-AP STAs perform UL soundingsimultaneously, the procedures described above may be performedindependently for each non-AP STA.

Some implementations provide channel access with synchronization for DLcoordinated SU and MU beamforming. Such examples may address issuesrelating to DL coordinated SU beamforming or joint precoding discussedearlier. In an example scenario where both AP1 and AP2 transmitconcurrently to a STA, the APs may need to synchronize with the STA suchthat the signals reach the STA with similar received power.Synchronization in time and frequency may also be needed in someimplementations. Accordingly, various techniques discussed with respectto FIG. 12 may be used to synchronize the transmissions from multipleAPs in some implementations.

FIG. 12 shows an exemplary channel access procedure which may allowmultiple APs to transmit to a STA concurrently. In the example of FIG.12 , AP1 and AP2 may negotiate to perform concurrent transmission to aSTA. In some examples, in the negotiation, AP1 may be considered as theprimary AP, and AP2 may be considered as the secondary AP. In someimplementations, the AP1 and AP2 may perform multi-AP joint transmissionsounding in advance or instantaneously to acquire channel stateinformation.

As shown in FIG. 12 , AP1 may acquire the channel and may transmit amulti-AP Trigger frame (i.e., trigger frame 1210) to trigger atransmission to a STA. AP1 may configure the upcoming multi-APtransmission in the multi-AP Trigger frame. In some implementations AP1,the primary AP, may configure the transmission from AP2 to the STA. Themulti-AP trigger frame may indicate, for example, STA specificinformation, and/or common information. STA specific information (whereSTA here indicates an AP STA or a non-AP STA) may indicate a STA roleand/or STA ID. The STA role may indicate whether the STA is atransmitter/AP or a receiver/STA. The STA ID may be the associationidentifier (AID), compressed AID, BSS identifier (BSSID, compressedBSSID), BSS color, or enhanced BSS color, etc.

If the STA role indicates a transmitter/AP, it may include a packet ID,resource allocation, spatial stream allocation, or MCS-relatedinformation. A packet ID may be used to indicate the packet transmittedfrom the STA. In some implementations, this field may be anAP/transmitter specific field. The STA may detect the packet IDscorresponding to multiple APs and determine whether a single packet istransmitted from multiple APs or multiple packets are transmitted frommultiple APs. In the first case, the STA may combine the transmissionsfrom multiple APs to decode the single packet. A resource allocation maybe used to indicate the resources allocated to the AP to transmit themulti-AP packet. In an OFDMA transmission scenario, the resource may beallocated in units of resource unit (RU). A spatial stream allocationmay be used to indicate the starting spatial stream index and number ofspatial streams used for the transmitter. MCS-related information thismay include MCS, coding scheme, whether DCM modulation is utilized etc.

Common information may include a type field. The type may indicate a DLmulti-AP transmission. The type may indicate a trigger frame transmittedfrom an AP.

In the case of multi-AP MU-MIIMO, the multi-AP trigger frame or framesmay include a list of all of the STAs to be transmitted to (see e.g.,FIG. 15 and FIG. 16 )

As shown in FIG. 12 , After reception of the multi-AP Trigger frame, theSTA may transmit an inverse trigger frame 1220 to multiple APs. In theinverse trigger frame 1220, the STA may indicate repeating full orpartial information carried by the trigger frame 1210 transmitted byAP1. This field may be used, for example, if AP1 and AP2 have difficultyin communicating with each other directly. This information may beprovided opportunistically or one of the APs may instruct the other.Alternatively, one of the APs may instruct the other opportunisticallyas needed. In the inverse trigger frame 1220, the STA may also oralternatively indicate synchronization related information, such aspower control information. In some such power information, the STA mayindicate the transmit power of the inverse trigger frame 1220, and/or anexpected received signal strength indicator (RSSI) for the multi-AP datatransmission. The APs may use these two fields to decide its owntransmit power. It is noted that in the case of a power imbalancebetween AP1 and AP2, the STA may request that the transmission from oneof the STAs be turned off, resulting in single AP transmission. In theinverse trigger frame 1220, the STA may also or alternatively indicatesynchronization related information, such as time and/or frequencycorrection information. In some such time and/or frequency correctioninformation, the STA may request one or more of the APs to perform atime and/or frequency correction relative to the trigger frame. It isnoted that the inverse trigger frame scheme may be extended to multi-APMU-MIMO, with each STA in the MU-MIMO set transmitting an independenttrigger either sequentially (see e.g., FIG. 14 ) or concurrently (seee.g., FIG. 13 ).

As shown in FIG. 12 , The STA may receive data transmissions (i.e., Data1 and Data 2) from AP1 and AP2. Depending on the Packet IDs in triggerframe 1210, the STA may or may not combine the transmissions. The STAmay transmit acknowledgement frames to the AP.

In the example of FIG. 12 , AP1 and AP2 may negotiate to performconcurrent transmission to a STA. In some implementations, in thenegotiation, AP1 may be considered as the primary AP and AP2 may beconsidered as the secondary AP. In some implementations, AP1 and AP2 mayperform multi-AP joint transmission sounding before and acquire thenecessary channel state information.

FIG. 13 illustrates an example channel access scheme which mayfacilitate multiple APs to transmit to a STA concurrently, where STAstransmit independent trigger frames concurrently, e.g., using UL OFDMAand/or UL MU-MIMO.

As shown in FIG. 13 , AP1 transmits a trigger frame 1310 to both STA1and STA2. Then, STA1 transmits an inverse trigger frame 1320 to both AP1and AP2. STA2 transmits an inverse trigger frame 1330 to both AP1 andAP2. Both the inverse trigger frame 1320 and the inverse trigger frame1330 are transmitted concurrently. Then, after receiving data from AP1and AP2, STA1 may transmit an ACK 1340 to both AP1 and AP2, and STA2 maytransmit an ACK 1350 to both AP1 and AP2.

FIG. 14 illustrates an example channel access scheme which mayfacilitate multiple APs to transmit to a STA concurrently, where STAstransmit independent trigger frame sequentially, e.g., using UL OFDMAand/or UL MU-MIMO.

As shown in FIG. 14 , AP1 transmits a trigger frame 1410 to both STA1and STA2. Then, STA1 transmits an inverse trigger frame 1420 to both AP1and AP2. STA2 transmits an inverse trigger frame 1430 to both AP1 andAP2. Both the inverse trigger frame 1420 and the inverse trigger frame1430 are transmitted sequentially. Then, after receiving data from AP1and AP2, STA1 may transmit an ACK 1440 to both AP1 and AP2, and STA2 maytransmit an ACK 1450 to both AP1 and AP2.

A method of multi-AP communication according to this application isdescribed with reference to FIGS. 15-18 as follows. The method ofmulti-AP communication according to this application may be performed bya WTRU.

FIG. 15 illustrates an exemplary multi-AP communication procedureaccording to an embodiment of this application. FIG. 16 illustrates anexemplary multi-AP MU-MIIMO communication procedure according to anembodiment of this application. FIG. 17 illustrates an exemplarymulti-AP MU-MIIMO communication procedure according to anotherembodiment of this application. FIG. 18 is a flowchart illustrating amethod 1800 of multi-AP communication according to an embodiment of thisapplication.

The method of multi-AP communication according to embodiments in thisapplication may be applied to multi-AP communication between multipleAPs and a STA. In other words, the method may be applied in a scenariowhere a plurality of APs have been deployed. Accordingly, the apparatus(e.g., a WTRU) for multi-AP communication according to embodiments inthis application may also be applied in a scenario where multiple APshave been deployed in order to transmit data between the APs and theSTA.

The method of multi-AP communication according to embodiments in thisapplication may also be applied in a scenario with multiple APs andmultiple STAs. In other words, the method may be applied in a scenariowhere a plurality of APs and a plurality of STAs have been deployed.Accordingly, the apparatus (e.g., a WTRU or WTRUs) for multi-APcommunication according to embodiments in this application may also beapplied in a scenario where a plurality of APs and a plurality of STAshave been deployed in order to transmit data between the APs and theSTAs.

The following embodiments will first describe a scenario where aplurality of APs and a STA have been deployed with reference to FIG. 15and FIG. 18 , and then describe a scenario where both a plurality of APsand a plurality of STAs have been deployed with reference to FIG. 16 andFIG. 17 .

Method 1800 according to an embodiment of this application will bedescribed in detail with reference to FIG. 15 and FIG. 18 as follows.Method 1800 is a method of multi-AP communication that may be applied inWLANS. It will be appreciated that Method 1800 may also be applied inother wireless transmission fields, such as WIFI and VPMN. Theabove-mentioned technical fields for the application of Method 1800 isdescribed only by way of example, and they are not intended to beexclusive or be limiting to the present application.

Method 1800 comprises: at 1801, receiving a first trigger frame from afirst AP of a plurality of APs, the first trigger frame comprising firstinformation; at 1802, receiving a second trigger frame from a second APof the plurality of APs at a predetermined time duration after receivingthe first trigger frame, the second trigger frame also comprising thefirst information of the first trigger frame; at 1803, generating asynchronization frame based on the first trigger frame and the secondtrigger frame, the synchronization frame comprising synchronizationinformation; at 1804, transmitting the synchronization frame to at leastthe first AP and the second AP; and at 1805, receiving a datatransmission based on the synchronization information from each of thefirst AP and the second AP. The above processes will be described indetails with reference to embodiments as follows.

The following description will describe the process at 1801 in moredetail. Method 1800 may be applied in a scenario where two APs have beendeployed, e.g., AP1 and AP2 (as shown in FIG. 15 ). Accordingly, theapparatus for multi-AP transmission according to embodiments in thisapplication may also be applied in a two-AP scenario, such as thescenario in FIG. 15 .

In a scenario with two APs, one may be a master AP or a primary AP, andanother one may be a slave AP or a secondary AP. As shown in FIG. 15 ,AP1 and AP2 may negotiate and determine that AP1 is the master AP andAP2 is the slave AP. AP1 and AP2 may perform multi-AP joint transmissionsounding before and acquire any necessary channel state information. Forthe purpose of a clear and definite description of this application,unless otherwise indicated, the terms “AP1”, “master AP” and “primaryAP” are used interchangeably in this application, and the terms “AP2”,“slave AP” and “secondary AP” are used interchangeably in thisapplication.

Although the example shown in FIG. 15 only illustrates two APs, it isonly described by way of example and it is not intended to be exclusiveand be limiting to embodiments of this application. For example, Method1800 may also be applied in a scenario having three APs, i.e., a firstAP, a second AP and a third AP. Accordingly, the apparatus (e.g., aWTRU) for multi-AP communication according to embodiments in thisapplication may also be applied in the above-mentioned three-APscenario.

The number of APs in embodiments of this application might be evengreater than three. Embodiments of this application does notspecifically limit the number of APs. It will be appreciated that thenumber of APs may vary based on many variables, such as a demand forupcoming data transmission between APs and STAs, a wireless transmissiontechnology used and the number of STAs.

As shown in FIG. 15 , in one embodiment, AP1 may acquire a channel andtransmit the first trigger frame 1510 (i.e., a multi-AP trigger frame)to the STA.

The first trigger frame 1510 sent by AP1 may be used to trigger atransmission from other APs and/or STAs. FIG. 15 illustrates anembodiment of multi-AP downlink transmission (i.e., Data 1 and Data 2)from AP1 and AP2 to the STA. Therefore, in the multi-AP downlinktransmission scenario, the first trigger frame 1510 may be used toconfigure a data transmission (i.e., Data 1) from AP1 to the STA.Further, the first trigger frame 1510 may also be used to configure adata transmission (i.e., Data 2) from AP2 to the STA. In order tosynchronize both data transmissions, the first trigger frame 1510 may beused to trigger a second trigger frame (e.g., second trigger frame 1520)to be sent by AP2 and a synchronization frame (e.g., synchronizationframe 1530) to be sent by the STA.

It should be noted that a trigger frame sent by AP1 may also be used toconfigure an uplink transmission as shown in FIG. 19 and FIG. 20 , Forexample, in an embodiment shown in FIG. 19 , a trigger frame 1910 may beused to trigger an inverse trigger frame (e.g., inverse trigger frame1920) to be sent by STA. In an embodiment shown in FIG. 20 , a triggerframe 2010 may be used to trigger a second trigger frame (e.g., shorttrigger frame 2020) to be sent by AP2 and an inverse trigger frame(e.g., inverse trigger frame 1920) to be sent by STA. Those embodimentsshown in FIG. 19 and FIG. 20 will be described in detail later.

The first trigger frame 1510 may also be used to indicate the STA howmany spatial streams and which modulation and coding scheme (MCS) to usewhen transmitting on the assigned RUs. Because the first trigger frame1510 is sent by the master AP (i.e., AP1), unless otherwise indicated,the term “first trigger frame” may also be referred to as “mastertrigger frame.”

The first trigger frame 1510 may comprise one or any combination of thefollowing information as its first information: RU allocationinformation, STA-specific information, and common information, etc. Itwill be appreciated that those above information carried by the firsttrigger frame 1510 may be configured into different fields. For example,the RU allocation information may be configured in a RU allocationinformation field; the STA-specific information may be configured in oneor more STA Information fields; and the common information may beconfigured in a common information field. When some specific informationcarried by the first trigger frame 1510 is described in the followingdescription, it means the information configured in a specific field.

The STA-specific information may comprise a STA role or a STA ID. TheSTA ID may indicate whether the STA is a transmitter (e.g., AP1 shown inFIG. 15 ) or a receiver (e.g., the STA shown in FIG. 15 ). It will beappreciated that generally speaking, WTRUs (e.g., the STA shown in FIG.15 ) and APs (e.g., AP1 shown in FIG. 15 ) may be referred to as STAs.For example, in a scenario of WLANS, a router (e.g., an AP) may bereferred to as a station, and a laptop (e.g., a STA) may also bereferred to as a station. The STA ID here in this application mayindicate whether a station is an AP STA (e.g., AP1 shown in FIG. 15 ) ora non-AP STA (e.g., the STA shown in FIG. 15 ).

The STA ID may be an AID, a compressed AID, a BSSID, a compressed BSSID,a BSS color, or an enhanced BSS color, etc.

If the STA ID indicates a transmitter (e.g., AP1), then the firsttrigger frame 1510 may further comprise one or any combination of thefollowing fields: a packet ID field, a resource allocation field, aspatial stream allocation field, and a MCS related information field.

The packet ID field may be used to indicate a packet transmitted to theSTA. In some embodiments, the packet ID field may be a transmitter/APspecific field. The STA may detect multiple packet IDs carried by thepacket ID field corresponding to the multiple APs and determine whethera single packet is transmitted from multiple APs or multiple packets aretransmitted from multiple APs. In some embodiments, the STA may combinethe transmissions from multiple APs to decode the single packet.

The resource allocation field may be used to indicate the resourcesallocated to the AP1 to transmit the multi-AP packet. In an OFDMAtransmission scenario, the resource may be allocated in units ofresource unit (RU).

The spatial stream allocation field may be used to indicate a startingspatial stream index and the number of spatial streams used for thetransmitter (i.e., AP1).

The MCS-related information field may include MCS, coding scheme, andinformation to indicate whether DCM modulation is utilized, etc.

The common information may comprise a type field. The type field mayindicate a DL multi-AP transmission. The type field may also indicate atrigger frame transmitted from an AP. In the case of multi-AP MU-MIMOcommunication, a multi-AP trigger frame or frames may contain a list ofall the STAs to which to transmit (see e.g., FIG. 16 and FIG. 17 ).

The first trigger frame 1510 may further comprise at least one of thefollowing information as its first information: transmission powerinformation, transmission starting time information, transmissionfrequency information, etc. Accordingly, those information may also beconfigured into different fields in order for the first trigger frame tocarry.

For example, the first trigger frame 1510 may comprise a power field toindicate a transmission power of a upcoming data transmission from AP1to the STA. The first trigger frame 1510 may also comprise a time fieldto indicate a starting time of a upcoming data transmission from AP1 tothe STA. The first trigger frame may also comprise a frequency field toindicate a transmission frequency of a upcoming data transmission fromAP1 to the STA.

For another example, the first trigger frame 1510 may further comprisetransmission starting time information for transmitting thesynchronization frame 1530 from the STA. In other words, the firsttrigger frame 1510 may indicate a starting time for transmitting thesynchronization frame 1530 shown in FIG. 15 from the STA. The startingtime information may also be configured into a specific field of thefirst trigger frame in order for it to carry.

Although the above description illustrated some exemplary embodiments ofthe first information in the first trigger frame 1510, those embodimentsare not intended to be exclusive or be limiting to the firstinformation. The first information described in the present applicationmay include any combination of the above-mentioned exemplary informationor any other information available to obtain the technical solution ofthis application.

Further, the first information of the first trigger frame is a relativeterm comparing to those terms “a second information of the first triggerframe” and “a third information of the first trigger frame”. In thisapplication, using those terms does not mean that the first information,the second information and the third information are completelydifferent information. In some embodiments, they may share the sameinformation between each other. Their relationship will be furtherdescribed in detail below.

Those information carried by the first trigger frame may be used fordata transmission synchronization between the multiple APs (e.g., AP1and AP 2 shown in FIG. 15 ) and the STA. It will be appreciated that theterm “synchronization” in this application means synchronizing one ormultiple parameters of the upcoming data transmissions, such as asynchronization in transmission power, a synchronization in transmissionstarting time, and a synchronization in transmission frequency. In otherwords, those parameters to be synchronized for the upcoming datatransmissions may comprise the transmission power, the transmissionstarting time and the transmission frequency.

For example, the transmission power information carried by the firsttrigger frame may be used for pre-correcting transmission power from themultiple APs to the STA so that those signals (e.g., data transmissions)from the APs may reach the STA with similar received powers. Thetransmission starting time information carried by the first triggerframe may be used for pre-correcting transmission starting time from themultiple APs to the STA so that those signals from the APs may reach theSTA with similar received time. The transmission frequency informationcarried by the first trigger frame may be used for pre-correctingtransmission frequency from the multiple APs to the STA so that thosesignals from the APs may reach the STA with similar receivedfrequencies.

It will be appreciated that the above-mentioned three parameters formulti-AP transmission are described only in way of example, and they arenot intended to be exclusive or be limiting to the present application.For example, the first trigger frame 1510 may be used to synchronize anycombination of those three parameter for the upcoming data transmission.

It will be appreciated that the synchronization described in thisapplication may not be obtained through the first trigger frame 1510alone. The first trigger frame 1510 is an essential part of thesynchronization, but Method 1800 and the apparatus (e.g., a WTRU)according to this application still need the second trigger frame 1520and the synchronization frame 1530 (described below) to obtain thesynchronization. For example, as shown in FIG. 15 , after receiving thefirst trigger frame 1510, the STA may send the synchronization frame1530 to the multiple APs, and the synchronization frame 1530 may carrysynchronization information which is necessary for synchronizing theupcoming data transmissions respectively from the multiple APs. Thefollowing description will describe the second trigger frame 1520 andthe synchronization frame 1530 in more detail.

In an embodiment, the first trigger frame 1510 may also be sent to otherAPs, such as AP2 shown in FIG. 15 , that is, the first trigger frame1510 from AP1 can be overheard by all STAs shown in FIG. 15 other thanAP1. Therefore, the first trigger frame 1510 may be used to configure aparameter or multiple parameters of a upcoming data transmission (i.e.,data 2 shown in FIG. 15 ) from AP2 to the STA. Since both the upcomingdata transmissions respectively from AP1 and AP2 may be configured bythe first trigger frame 1510, the upcoming data transmissions from bothAP1 and AP2 may be synchronized accordingly. The following descriptionwill describe how to use the first trigger frame 1510 to configure theupcoming data transmission from AP 2 with reference to the process at1802.

In an embodiment with more than two APs, AP1 may send the first triggerframe to all other APs. Based on a principle similar to that illustratedabove, all upcoming data transmission from these APs may be synchronizedaccordingly.

In order to receive the first trigger frame from AP1, the STA may beconfigured to comprise a receiver. The receiver may be a USB receiver, awireless LAN receiver or any other kind of receiver that may be used toreceive a signal transmitted within a WLAN scenario shown in FIG. 15 andFIG. 4 .

For the purpose of clear and definite description of the embodiments inthis application, unless otherwise indicated, an upcoming datatransmission from AP1 to the STA may be referred to as a first datatransmission, and an upcoming data transmission from AP 2 to the STA maybe referred to as a second data transmission. As shown in FIGS. 15-17 ,the first data transmission may be referred to as Data 1, and the seconddata transmission may be referred to as Data 2.

The following description will describe the process at 1802 in moredetail. As described above, AP1 may also send the first trigger frame1510 to AP 2. After receiving the first trigger frame 1510, AP2 maygenerate and transmit a second trigger frame 1520 to the STA. Because itmay take some time for the first trigger frame 1510 to be transmittedfrom AP1 to AP2, and it may also take some time for AP2 to generate thesecond trigger frame 1520, there may be a time duration (i.e., SIFSshown in FIG. 15 ) between the time of transmitting the first triggerframe 1510 and the time of transmitting the second trigger frame 1520.Accordingly, at the STA side, there may be a time duration-SIFS betweenthe time of receiving the first trigger frame 1510 and the time ofreceiving the second trigger frame 1520. That is to say, the STA mayreceive the first trigger frame 1510 first, and then after the timeduration-SIFS, the STA may receive the second trigger frame 1520.

As shown in FIG. 15 , three blocks respectively representing the firsttrigger frame 1510, the second trigger frame 1520 and thesynchronization frame 1530 are located at three different horizontallines, each of which represents one of AP1, AP2 and the STA. Althoughthese blocks are located at different places in the vertical direction,it will be appreciated that they are only illustrated in this way forthe purpose of showing a source of each frame, and their projections inthe horizontal direction may represent the time of receiving each frameat the STA side.

The time duration may be predetermined through some existing parameters.For example, the time duration may be predetermined based on thedistance between AP1 and AP2, and a length of time for AP 2 to generatethe second trigger frame. In other words, as long as the distancebetween AP1 and AP2 is already known and the length of time forgenerating the second trigger frame is already known, the time durationmay be known.

In embodiments, once AP1 and AP2 have been constructed, the distancebetween them may be fixed and thus known. Further the hardware thatconstitutes the APs may also be fixed after their construction.Therefore, the length of time for generating the second trigger framemay also be known. Thus, the time duration may be predetermined afterthe construction of the APs.

The time duration SIFS may be predetermined by AP1 and/or AP2. Forexample, the time duration may be predetermined by AP1. In that case,the first trigger frame 1510 may further comprise a time-duration fieldto carry time duration information. The time duration information mayindicate when AP2 should send out the second trigger frame 1520 afterits reception of the first trigger frame 1510. Then, after AP 2 receivesthe first trigger frame 1510, it will generate and send out the secondtrigger frame 1520 based on the time duration information. It will beappreciated that in that case, the time duration SIFS indicated by thetime duration information should be longer than a length of time fortransmitting the first trigger frame 1510 from AP1 to AP2 plus a lengthof time for AP 2 to generate the second trigger frame 1520.

In an embodiment, the time duration (i.e., SIFS shown in FIG. 15 ) maybe predetermined through any inter-frame spacing, e.g., short IFS(SIFS), point coordination function (PCF) IFS (PIFS), distributedcoordination function (DCF) IFS (DIFS), etc.

The second trigger frame may comprise the above-mentioned firstinformation of the first trigger frame 1510.

The first information of the first trigger frame 1510 may be informationwhich may be shared with the second trigger frame 1520. For example, thefirst information of the first trigger frame is the above-mentionedcommon information which indicates a DL multi-AP transmission. Then, AP2 can directly copy that information into the second trigger frame 1520.

In an embodiment, the first information of the first trigger frame 1510may be transmission power information for an upcoming data transmissionfrom AP1 to the STA. Then, AP2 determines that the transmission powerindicated by the transmission power information is within itstransmission power limitation. Therefore, AP 2 may directly write thetransmission power information into the second trigger frame 1520.

It will be appreciated that the above-mentioned embodiments of thesecond trigger frame 1520 are merely described by way of example, andthey are not intended to be exclusive or be limiting to the presentapplication.

In embodiments, the second trigger frame 1520 may be generated to be anyone of the following formats: for format (1), the second trigger frame1520 is the same as the first trigger frame 1510, i.e., the secondtrigger frame 1520 comprises all of the information of the first riggerframe 1510; for format (2), the second trigger frame 1520 is a subset ofthe first trigger frame 1510, i.e., the second trigger frame 1520 onlycomprises a part of information of the first trigger frame 1510 (e.g.,the above-mentioned first information of the first trigger frame 1510);and for format (3), the second trigger frame 1520 comprises both a partof information of the first trigger frame 1510 (e.g., theabove-mentioned first information of the first trigger frame 1510) andconfiguration information for an upcoming data transmission (i.e., Data2) from AP2.

In an embodiment, the configuration information in the second triggerframe 1520 may be different from a second information of the firsttrigger frame 1510. For example, the first trigger frame 1510 mayindicate AP2 to use a particular channel (e.g., channel 2) for anupcoming data transmission (i.e., Data 2) to the STA. That is, thesecond information of the first trigger frame 1510 may be information ofthe channel 2 to be used by AP2 for the second data transmission.However, AP2 may figure out that the channel 2 is not available for itto do the transmission. In that case, AP 2 may transmit a second triggerframe 1520 with a configuration information to both AP1 and the STA toindicate that the channel 2 is unavailable. In that case, theconfiguration information (i.e., the channel 2's unavailability) isdifferent from the second information of the first trigger frame 1510(i.e., the choice of the channel 2).

In the above example, if AP2 figures out that the channel 2 is notavailable but another channel (e.g., a channel 3) is available for it todo the data transmission. Then, AP2 may transmit a second trigger framewith a configuration information to both AP1 and the STA to indicatethat the channel 2 is unavailable and that AP2 will use the channel 3for the upcoming data transmission from AP 2 to the STA. In that case,the configuration information (i.e., the channel 2's unavailability andthe choice of the channel 3) is different from the second information ofthe first trigger frame 1510 (i.e., the choice of the channel 2). Inother words, the configuration information may overwrite the secondinformation of the first trigger frame 1510.

For example, the first trigger frame 1510 may indicate AP2 to use aparticular transmission power for an upcoming data transmission (i.e.,Data 2) to the STA. That is, the second information of the first triggerframe 1510 may be information of a transmission power (e.g., atransmission power 2) to be used by AP2 for the second datatransmission. However, AP2 may figure out that the transmission power 2is beyond a power limitation of AP2. In that case, AP2 may transmit asecond trigger frame with a configuration information to both AP1 andthe STA to indicate that the transmission power 2 is unavailable andthat AP2 will use its desired transmission power (e.g., a transmissionpower 3) for the second data transmission. In that case, theconfiguration information (i.e., the transmission power 2'sunavailability and the choice of the transmission power 3) is differentfrom the second information of the first trigger frame 1510 (i.e., thetransmission power 2). In other words, the configuration information mayoverwrite the second information of the first trigger frame 1510.

It will be appreciated that the above mentioned channels andtransmission powers are merely described by way of example, and they arenot intended to be exclusive or be limiting to the configurationinformation in the second trigger frame 1520. The configurationinformation may comprise other information as long as those informationmay be necessary to configure the second data transmission.

In an embodiment, the configuration information in the second triggerframe 1520 may be additional information not comprised in the firsttrigger frame 1510.

For example, the first trigger frame 1510 may comprise the transmissionpower information and the transmission starting time information, but notransmission frequency information. That is, the second information ofthe first trigger frame 1510 may be the transmission power informationand the transmission starting time information to be used by AP2 for thesecond data transmission. Then AP2 may send a second trigger frame 1520with a configuration information to both AP1 and the STA to indicate adesired transmission frequency of AP2 for the second data transmission.In that case, the configuration information (i.e., a desiredtransmission frequency of AP 2) is additional information not comprisedin the first trigger frame. In the above example, the STA may send asynchronization frame 1530 (further described below) with the desiredtransmission frequency of AP2 to both AP1 and AP2, and thus the APs maydo data transmissions by using the desired transmission frequency. Thus,the synchronization in transmission frequency may be obtained. Thesynchronization process will be further described below with referenceto the synchronization frame 1530 from the STA.

It will be appreciated that the above mentioned transmission frequencyare merely described by way of example for the configurationinformation, and they are not intended to be exclusive or be limiting tothe configuration information in the second trigger frame 1520. Theconfiguration information may comprise other information which has notbeen comprised in the first trigger frame 1510 as long as thoseinformation may be necessary for synchronizing the upcoming datatransmissions.

In embodiments, the second trigger frame 1520 may be an NDP frame whichmay carry AP2's identity. The NDP frame may indicate that AP 2 is readyfor the upcoming multi-AP transmission. The second trigger frame 1520may also comprise a starting time field indicating a transmissionstarting time for the transmission of the synchronization frame 1530.

As describe above, both WTRUs and APs may be referred to as STAs.Therefore, in an embodiment with more than two APs, the second triggerframe 1520 may also be sent to all other APs, that is, the secondtrigger frame 1520 from AP2 can be overheard by all STAs other than AP2,including both AP STAs and non-AP STAs. In an embodiment with multipleAP STAs and multiple non-AP STAs shown in FIG. 16 , a second triggerframe may also be sent to all STAs.

In an embodiment, multiple APs may transmit trigger frames sequentially,and an order of trigger frame transmission may be negotiated between themultiple APs using a management/control frame. For example, assumingthat a management/control frame indicates that AP1 may transmit atrigger frame (e.g., first trigger frame 1510) first and then AP2 maytransmit a trigger frame (e.g., second trigger frame 1520) second.

In an embodiment, the order of the trigger frame transmission may bepredefined by a predetermined rule. For example, AP1, the primary AP,may transmit the trigger frame first. The rest of the multiple APs maytransmit in the ascending/descending order based on the BSSID or AP MACaddress. It will be appreciated that all the APs in the group may knowthe member AP BSSIDs or MAC addresses.

The following description will describe the process at 1803 in moredetail. After receiving both the first trigger frame 1510 and the secondtrigger frame 1520, the STA shown in FIG. 15 may generate asynchronization frame 1530 based on the first and second trigger frames.the synchronization frame 1530 comprises a synchronization informationto configure a data transmission from each of AP1 and AP2 to the STA.

Similar to the first trigger frame 1510, the synchronization frame 1530may comprise one or any combination of the following information: RUallocation information, STA-specific information, and commoninformation, etc. Those above information carried by the synchronizationframe 1530 may be configured into different fields.

The synchronization frame 1530 may further comprise transmission powerinformation, transmission starting time information, transmissionfrequency information, etc. Accordingly, those information may also beconfigured into different fields in order for the synchronization frame1530 to carry. The above-mentioned information may be referred to assynchronization information which may be used to configure an upcomingdata transmission from each of AP1 and AP2 to the STA.

It will be appreciated that the above-mentioned information comprised inthe synchronization frame 1530 is only described by way of example, andit is not intended to be exclusive or be limiting to those informationwhich may be comprised in the synchronization frame 1530.

In order to generate the synchronization frame 1530, the apparatus(e.g., a WTRU) according to this application comprises a processor. Asshown in FIG. 15 , the processor is configured to generate thesynchronization frame 1530 based on the first and second trigger framesrespectively received from AP1 and AP2.

In embodiments, the synchronization frame 1530 may share the same formatwith the first trigger frame 1510. In other words, the synchronizationframe 1530 may be generated to be any one of the following formats: forformat (1), the synchronization frame 1530 is the same as the firsttrigger frame 1510, i.e., the synchronization frame 1530 comprises allof the information of the first rigger frame 1510; for format (2), thesynchronization frame 1530 is a subset of the first trigger frame 1510,i.e., the synchronization frame 1530 only comprises a part ofinformation of the first trigger frame 1510; and for format (3), thesynchronization frame 1530 comprises both a part of information of thefirst trigger frame and confirmation information.

For the format (1) and the format (2), the synchronization frame 1530may comprise a full or partial information carried by the first triggerframe 1510 transmitted by AP1. This full or partial information may bebeneficial. For example, if AP1 and AP2 may have difficulty incommunicating with each other directly, then the STA may transmit thoseinformation originated from AP1 to AP2 for the purpose of datatransmission synchronization.

For the format (3), the confirmation information may be used to confirmthose information carried by the first trigger frame 1510 and/or thesecond trigger frame 1520. The confirmation information may also be usedto confirm any configuration modification by AP2. The confirmedconfiguration may be based on the first trigger frame 1510 or the secondtrigger frame 1520 or a combination of the first trigger frame 1510 andthe second trigger frame 1520.

For example, if the first trigger frame 1510 indicates that atransmission power for the first data transmission is power 1, and thesecond trigger frame 1520 indicates that a transmission power for thesecond data transmission is also power 1, then the confirmationinformation may be used to confirm to both AP1 and AP2 that they may usethe power 1 for their upcoming data transmissions. Meanwhile, if thefirst trigger frame 1510 comprises a group of information comprising aspatial stream allocation and a MCS-related information, then, thisgroup of information may be referred to as the third information of thefirst trigger frame 1510 which may be comprised into the synchronizationframe 1530.

In embodiments, the synchronization frame 1530 may share the same formatas that of the second trigger frame 1520. In other words, thesynchronization frame 1530 may be generated to be any one of thefollowing formats: for format (1), the synchronization frame 1530 is thesame as the second trigger frame 1520, i.e., the synchronization frame1530 comprises all of the information of the second rigger frame 1520;for format (2), the synchronization frame 1530 is a subset of the secondtrigger frame 1520, i.e., the synchronization frame 1530 only comprisesa part of information of the second trigger frame 1520; and for format(3), the synchronization frame 1530 comprises both a part of informationof the second trigger frame 1520 and confirmation informationcorresponding to the above-mentioned configuration information in thesecond trigger frame 1520.

For the format (1) and the format (2), the synchronization frame 1530may comprise a full or partial information carried by the second triggerframe 1520 transmitted by AP 2. This full or partial information may bebeneficial. For example, if AP1 and AP2 may have difficulty incommunicating with each other directly, then the STA may transmit thoseinformation originated from AP2 to AP1 for the purpose of datatransmission synchronization.

For the format (3), the confirmation information may be used to confirmany configuration modification by AP2. The confirmed configuration maybe based on the first trigger frame 1510 or the second trigger frame1520 or a combination of the first trigger frame 1510 and the secondtrigger frame 1520.

As shown in FIG. 15 , the synchronization information may be used tosynchronize a parameter or multiple parameters of the first datatransmission from AP1 with a parameter or multiple parameters of thesecond data transmission from AP2. In an embodiment, the synchronizationinformation comprises transmission power information, transmissionstarting time information and transmission frequency information.

For example, the synchronization information may comprise transmissionfrequency information. In that case, the first trigger frame 1510received from AP1 may indicate that a transmission frequency for thefirst data transmission may be a frequency 1, and the second triggerframe 1520 received from AP 2 may indicate that a transmission frequencyfor the second data transmission may be a frequency 2. Then, the STA maygenerate a synchronization frame 1530 with particular transmissionfrequency information to indicate a desired transmission frequency forboth of the upcoming data transmissions. AP1 and AP2 may do the upcomingdata transmissions based on the desired transmission frequency.

In an embodiment with more than two APs and one STA, a synchronizationframe from the STA may be configured to synchronize a parameter (ormultiple parameters) of a upcoming data transmission from each of themultiple APs.

It will be appreciated that according to the embodiments of thisapplication, the synchronization process of upcoming data transmissionsfrom multiple APs might not be completed by the synchronization frame1530 alone, and it needs frame interactions between the STA and the APs.Based on the above description, the synchronization process may beachieved by the first trigger frame 1510, the second trigger frame 1520and the synchronization trigger frame 1530.

At 1804, the STA may send the synchronization frame 1530 to both AP1 andAP2. In an embodiment with more than two APs and one STA, at 1804, theSTA may send the synchronization frame 1530 to at least AP1 and AP2.However, the embodiment shown in FIG. 15 is not intended to be exclusiveor be limiting to the principle of this application. For example, theSTA may select that only AP1 or only AP2 may transmit data to the STA.The AP down-selection may depend on the information carried in thetrigger frames transmitted from AP1 and AP2 or the STA measurement basedon the transmission from AP1 and AP2. For example, if a received SNR(i.e., Signal to Noise Ratio) or RSSI from one AP is lower than apredefined/predetermined threshold, then the STA may exclude that APfrom multi-AP transmission.

Based on the synchronization frame from the STA, AP1 may do the firstdata transmission to the STA and AP2 may do the second data transmissionto the STA. That is, at 1805, the STA may receive a data transmissionbased on the synchronization information from each of AP1 and AP2. Itshould be noted that the first and second data transmission from AP1 andAP2 may be concurrent using the same frequency resources (e.g. Multi-APMU-MIMO or Multi-AP nulling or coordinated SU/MU or coordinatednulling/beamforming), or using different frequency resources (e.g.Multi-AP OFDMA, coordinated OFDMA transmission)

In an embodiment, after receiving the first and second datatransmission, the STA may transmit an ACK/NACK report (i.e., ACK 1540shown in FIG. 15 ) to each of AP1 and AP2.

It is noted that the method of multiple-AP transmission according tothis application may be extended to multi-AP MU-MIMO with each STA inthe MU-MIMO set transmitting an independent trigger either sequentially(as shown in FIG. 16 ) or concurrently (as shown in FIG. 17 ).

FIG. 16 illustrates an exemplary multi-AP MU-MIIMO communicationprocedure according to an embodiment of this application.

As shown in FIG. 16 , a STA1 may receive a first trigger frame 1610 fromAP1, and may receive a second trigger frame 1620 from AP2. Then, theSTA1 may generate a synchronization frame 1630 based on the firsttrigger frame 1610 and the second trigger frame 1620, and then transmitthe synchronization frame 1630 to both AP1 and AP2. A STA2 may receive afirst trigger frame 1610 from AP1, and may receive a second triggerframe 1620 from AP2. Then, the STA2 may generate a synchronization frame1640 based on the first trigger frame 1610 and the second trigger frame1620, and then transmit the synchronization frame 1640 to both AP1 andAP2.

As shown in FIG. 16 , the STA1 may transmit the synchronization frame1630 first, and then the STA2 may transmit the synchronization frame1640. The first trigger frame 1610 is similar to or the same as thefirst trigger frame 1510 shown in FIG. 15 . The second trigger frame1620 is similar to or the same as the second trigger frame 1520 shown inFIG. 15 . The synchronization frame 1630 and the synchronization frame1640 are similar to or the same as the synchronization 1530 shown inFIG. 15 .

As shown in FIG. 16 , after AP1 and AP2 receive the synchronizationframe 1630 and the synchronization frame 1640, AP1 and AP2 may transmitdata (i.e., Data 1 and Data 2 shown in FIG. 16 ) respectively to STA1and STA2. Then, STA1 may transmit ACK 1650 respectively to AP1 and AP2.STA2 may transmit ACK 1660 respectively to AP1 and AP2.

FIG. 17 illustrates an exemplary multi-AP MU-MIIMO communicationprocedure according to another embodiment of this application.

As shown in FIG. 17 , a STA1 may receive a first trigger frame 1710 fromAP1, and may receive a second trigger frame 1720 from AP2. Then, theSTA1 may generate a synchronization frame 1730 based on the firsttrigger frame 1710 and the second trigger frame 1720, and then transmitthe synchronization frame 1730 to both AP1 and AP2. A STA2 may receive afirst trigger frame 1710 from AP1, and may receive a second triggerframe 1720 from AP2. Then, STA2 may generate a synchronization frame1740 based on the first trigger frame 1710 and the second trigger frame1720, and then transmit the synchronization frame 1740 to both AP1 andAP2.

As shown in FIG. 17 , STA1 and STA2 may transmit their ownsynchronization frame at the same time. The first trigger frame 1710 issimilar to or the same as the first trigger frame 1510 shown in FIG. 15. The second trigger frame 1720 is similar to or the same as the secondtrigger frame 1520 shown in FIG. 15 . The synchronization frame 1730 andthe synchronization frame 1740 are similar to or the same as thesynchronization 1530 shown in FIG. 15 .

As shown in FIG. 17 , after AP1 and AP2 receive the synchronizationframe 1730 and the synchronization frame 1740, AP1 and AP2 may transmitdata (i.e., Data1 and Data 2 shown in FIG. 16 ) respectively to STA1 andSTA2. Then, STA1 may transmit ACK 1750 respectively to AP1 and AP2. STA2may transmit ACK 1760 respectively to AP1 and AP2.

It should be noted that the STA may receive data transmissions from AP1and AP2. In an embodiment with more than two APs, the STA may select oneAP or multiple APs to send the synchronization. Accordingly, only thoseAPs that have received the synchronization may do upcoming datatransmissions. Depending on the Packet IDs in multi-AP Trigger frame,the STA may or may not combine the transmissions. The STA may transmitacknowledgement frames to the AP.

The associated STA procedure is shown in FIG. 18 , where the STAreceives the master trigger. The master trigger identifies theparameters of the multi-AP transmission and the number of APs andadditional DL triggers to expect. STA receives the trigger informationfor the N−1 additional triggers. STA estimates parameters for each AP;e.g., Rx power, timing offset, and/or frequency offset. STA selectsparameters for multi-AP transmission. STA calculates multi-APtransmission parameters; e.g., Tx power, time and/or frequency offsetcorrection. STA sends a reverse trigger to the AP with suggestedmulti-AP transmission parameters. STA receives multi-AP transmissiondata. STA sends ACK to the AP.

Some implementations provide channel access for uplink coordinated SUbeamforming or UL dynamic point selection.

FIG. 19 illustrates an example channel access scheme which allowsmultiple APs to receive from a STA concurrently. As shown in FIG. 19 ,AP1 transmits a trigger frame 1910 to a STA. The trigger frame 1910 issimilar to or the same as the first trigger frame 1510 shown in FIG. 15. Then, the STA transmit an inverse trigger frame 1920 to both AP1 andAP2 based on the trigger frame 1910. Then, the STA transmits a Data 2 toboth AP1 and AP2. After receiving the Data 2, AP1 may transmit an ACK1930 to the STA, and AP2 may transmit an ACK 1940 to the STA. In thisexample, data may be addressed to both APs or to a specific AP (e.g., inthe case of dynamic point selection). The target AP or APs may beaddressed in the inverse trigger 1920. This example may address issuesrelating to UL coordinated SU beamforming or joint precoding.

In this example, a STA may transmit to multiple APs concurrently in UL.If the APs cannot receive from each other or cannot receive from theprimary AP, a channel access procedure may be implemented to inform allthe desired APs that the multi-AP UL transmission may be expected.

In this example, AP1 and AP2 may negotiate to perform concurrentreception from a STA. In some implementations, in the negotiation, AP1may be considered as the primary AP and AP2 may be considered as thesecondary AP. In some implementations, the AP1 and AP2 may performmulti-AP joint transmission sounding before and acquire the necessarychannel state information or may enable the STA perform sounding andacquire the channel between itself and the APs. In this case, the STAmay send an NDPA and NDP to the APs individually or in a joint mannerand then acquire the UL channel from each AP e.g. by polling each AP orby sending an UL Trigger for the APs to send their channel informationin a pre-determined manner e.g. DL Multi-AP transmission.

The channel access procedure for UL Multi-AP transmission may betriggered by one or more of the APs. In one method, AP1 and AP2 may notbe able to receive from one other and the negotiation may be through aSTA. In some implementations, AP1 may acquire the channel and transmit amulti-AP trigger frame to trigger a transmission from a STA. In themulti-AP trigger frame, AP1 may configure the upcoming UL multi-APtransmission in the multi-AP trigger frame. In some implementations,AP1, the primary AP, may configure the transmission from AP2 to the STA.For example, the multi-AP trigger frame may indicate STA specificinformation, and/or common information. STA specific information (whereSTA here indicates an AP STA or a non-AP STA) may indicate a STA roleand/or STA ID. The STA role may indicate whether the STA is atransmitter/AP or a receiver/STA. The STA ID may be the associationidentifier (AID), compressed AID, BSS identifier (BSSID, compressedBSSID), BSS color, or enhanced BSS color, etc.

If the STA role indicates a transmitter/STA, it may include a packet ID.The packet ID may indicate that the packet is transmitted from the STA.In some examples, this field may be an AP/transmitter specific field.The STA may detect the packet IDs corresponding to multiple APs anddetermine whether a single packet is transmitted from multiple APs ormultiple packets are transmitted from multiple APs. In the first case,the STA may combine the transmissions from multiple APs to decode thesingle packet.

If the STA role indicates a receiver/AP, it may include a resourceallocation, spatial stream allocation, and/or MCS related information. Aresource allocation may indicate the resources allocated to the STA totransmit the multi-AP packet to the AP. In an OFDMA transmissionscenario, the resource may be allocated in units of resource unit (RU).A spatial stream allocation may indicate the starting spatial streamindex and number of spatial streams used for the receiver. MCS relatedinformation may include MCS, coding scheme, whether DCM modulation isutilized etc.

Common information may include a type field. The type may indicate a ULmulti-AP transmission. The type may indicate a trigger frame transmittedfrom an AP.

After reception of the multi-AP trigger frames from AP1, the STA maytransmit an inverse Trigger frame to multiple APs. In the inversetrigger frame, the STA may indicate repeating full or partialinformation carried by multi-AP Trigger frame transmitted by AP1. Thisfield may be used, for example, if AP1 and AP2 have difficulty incommunicating with each other directly. In such cases, or if AP2modifies anything in its trigger frame, the inverse trigger frame mayconfirm a configuration to be used in the upcoming multi-APtransmission. The confirmed configuration may be from AP1 or AP2 or acombination of AP1 and AP2.

The STA may transmit data to AP1 and AP2. In some implementations, atthe end of the transmission, the STA may concatenate another inversetrigger frame to trigger the concurrent transmission of acknowledgementfrom the APs. In the inverse trigger frame, the STA may includesynchronization information, such as power control information. Thepower control information may indicate the transmit power of the inversetrigger frame, and/or expected RSSI for the multi-AP data transmission.The APs may use these two fields to decide their own transmit powers.The STA may request one or more of the APs to perform a time and/orfrequency correction relative to the trigger frame. The APs may transmitacknowledgement frames to the STA.

FIG. 20 illustrates an example channel access scheme which allowsmultiple APs to receive from a STA concurrently. As shown in FIG. 20 ,AP1 transmits a trigger frame 2010 to a STA. The trigger frame 2010 issimilar to or the same as the first trigger frame 1510 shown in FIG. 15. Then, AP2 transmits a short trigger frame 2020 which may comprise anavailability information to the STA. Then, the STA generates an inversetrigger frame 2030 based on the trigger frame 2010 and the short triggerframe 2020, and transmit the inverse trigger frame 2030 to both AP1 andAP2. Then, the STA transmits Data 2060 based on information in theinverse trigger frame 2030 to both AP1 and AP2. After receiving the Data2, AP1 may transmit an ACK 2040 to the STA, and AP2 may transmit an ACK2050 to the STA.

Data 2060 may be addressed to both APs or to a specific AP (e.g., in thecase of dynamic point selection). The target AP or APs may be addressedin the inverse trigger.

In some examples, the APs may be able to receive from one other. Achannel access scheme may be used to exchange multi-AP UL transmissioninformation and meanwhile protect the transmission from interferencefrom others. FIG. 20 illustrates another example channel accessprocedure which in some implementations may permit a STA to transmit tomultiple APs concurrently.

In the example of FIG. 20 , AP1 and AP2 may negotiate to performconcurrent reception from a STA. In some implementations, in thenegotiation, AP1 may be considered as the primary AP and AP2 may beconsidered as the secondary AP. In some examples, the AP1 and AP2 mayperform multi-AP joint transmission sounding in advance, and may acquirethe necessary channel state information. In some implementations, AP1and AP2 may not be able to receive from each other and the negotiationmay be through a STA.

AP1 may acquire the channel and transmit a multi-AP Trigger frame totrigger a transmission from a STA. In the multi-AP Trigger frame, AP1may configure the upcoming UL multi-AP transmission in the multi-APTrigger frame. In one method, we may allow AP1, the primary AP toconfigure the transmission from AP2 to the STA. For example, themulti-AP trigger frame may indicate STA specific information, and/orcommon information. STA specific information (where STA here indicatesan AP STA or a non-AP STA) may indicate a STA role and/or STA ID. TheSTA role may indicate whether the STA is a transmitter/AP or areceiver/STA. The STA ID may be the association identifier (AID),compressed AID, BSS identifier (BSSID, compressed BSSID), BSS color, orenhanced BSS color, MAC address, compressed MAC address, etc.

If the STA role may indicate a transmitter/STA, it may include a packetID. The packet ID may be used to indicate that the packet is transmittedfrom the STA. In some examples, this field may be an AP/transmitterspecific field. The STA may detect the packet IDs corresponding tomultiple APs and determine whether a single packet is transmitted frommultiple APs or multiple packets are transmitted from multiple APs. Inthe first case, the STA may combine the transmissions from multiple APsto decode the single packet.

If the STA role indicates a receiver/AP, it may include a resourceallocation, spatial stream allocation, and/or MCS related information. Aresource allocation may indicate the resources allocated to the STA totransmit the multi-AP packet to the AP. In an OFDMA transmissionscenario, the resource may be allocated in units of resource unit (RU).A spatial stream allocation may indicate the starting spatial streamindex and number of spatial streams used for the receiver. MCS relatedinformation may include MCS, coding scheme, whether DCM modulation isutilized etc.

Common information may include a type field. The type may indicate a ULmulti-AP transmission. The type may indicate a trigger frame transmittedfrom an AP. Common information may include time and/or frequencycorrection information, e.g., where the STA may request one or more ofthe APs to perform a time and/or frequency correction relative to thetrigger frame.

After reception of the multi-AP Trigger frame, AP2 may transmit amulti-AP trigger frame, which may be the same as the one transmitted byAP1. Alternatively, AP2 may transmit a short multi-AP trigger frame,which may carry a subset of information transmitted by AP1. In someimplementations, the short multi-AP Trigger frame may be an NDP frame,which may carry the identity of AP2. The transmission from AP2 mayindicate that AP2 is ready for the upcoming multi-AP transmission. Insome implementations, the multi-AP trigger frame or the short multi-APtrigger frame may overwrite some information transmitted by AP1. Forexample, AP2 may be assigned to use channel 2 to receive from the STA,however, channel 2 may not be available for AP2, AP2 may indicate eithernot available or available channel list to both AP1 and STA.

After reception of the multi-AP Trigger frames from multiple APs, theSTA may transmit an inverse trigger frame to multiple APs. In theinverse trigger frame, the STA may indicate repeating full or partialinformation carried by multi-AP trigger frame transmitted by AP1. Thisfield may be used, for example, if AP1 and AP2 have difficulty incommunicating with each other directly. In such cases, or if AP2modifies anything in its trigger frame, the inverse trigger frame mayconfirm a configuration to be used in the upcoming multi-APtransmission. The confirmed configuration may be from AP1 or AP2 or acombination of AP1 and AP2.

The STA may transmit data to AP1 and AP2. In some implementations, atthe end of the transmission, the STA may concatenate another inversetrigger frame to trigger the concurrent transmission of acknowledgementfrom the APs. In the inverse trigger frame, the STA may includesynchronization information. The synchronization information may includepower control information. The synchronization information may includetime and/or frequency correction information. The power controlinformation may indicate the transmit power of the inverse triggerframe, and/or expected RSSI for the multi-AP data transmission. The APsmay use these two fields to decide their own transmit powers. In thetime and/or frequency correction information the STA may request one ormore of the APs to perform a time or frequency correction relative tothe trigger frame. The APs may transmit acknowledgement frames to theSTA.

Some implementations provide Transmit power and Multi-User JointTransmission. Such examples may address issues relating to coordinatedMU beamforming, where APs have different impairments and/orconfigurations (e.g., different transmit powers and/or EVMs).

In some implementations, to resolve the problem of inverting a JTMU-MIMO channel with a high conversion number, the power component andthe effective channel may be inverted separately. In someimplementations, eliminating the power effect may make the resultingmatrix more invertible (e.g., have a lower condition number).

In some implementations, the inversion of the two components may beperformed in the baseband. In some implementations, the power descalingor inversion may be performed in the analog domain while the inversionof the rest of the channel may be done in the baseband (e.g., a combinedanalog and digital baseband JT MU-MIMO).

In some implementations of a combined analog and digital baseband JTMU-MIMO, the APs may send their Tx power values to the controller andthe controller may send the analog precoding power scaling values to theAPs. The APs may thereafter perform power scaling and commence JPprecoding procedures.

In some implementations of a combined analog and digital baseband JTMU-MIMO, the master AP may request that the slave AP report its transmitpower. The master AP may thereafter send the analog power scaling valueto the slave AP. FIG. 21 and FIG. 22 illustrate an example procedure andframe exchange for an example JT MU-MIMO procedure with explicitfeedback. FIG. 23 and FIG. 24 illustrate an example procedure and frameexchange for an example JT MU-MIMO procedure with implicit feedback.FIG. 21 and FIG. 23 illustrate JT procedures for an unbalanced powerscenario, where the master AP designs precoders. FIG. 22 and FIG. 24illustrates JT procedures for an unbalanced power scenario, where eachAP designs precoders.

In some implementations, APs and STAs coordinate to set the AP transmitpower and AP precoders with the precoders designed at the master AP. Insome implementations of a combined analog and digital baseband JTMU-MIMO, the APs may request for the effective JP channel, H, to be sentfrom the STAs. The master AP or controller may then normalize thecondition number of the effective channel and send separate analogscaling and digital precoding parameters to the APs for JP transmission.

An example of such procedure may be described as having setup,channel/power acquisition, precoder information, and transmissionstages. These are exemplary; the procedure may be implemented in anysuitable order or combination of stages.

During an example setup phase, each STA associates with multiple APs andidentifies the type of multi-AP transmission it is capable of (e.g., inthis case, joint-transmission). Both APs and STAs indicate that they arecapable of analog and digital processing for power imbalance. It isnoted that in cases where the capability is absent, the AP/STA may electto drop out of the multi-AP scheme and transmit/receive from a singleAP/STA.

During an example channel/power acquisition stage, the APs and STAundergo a sounding procedure to identify the effective MIMO channel.This may be explicit or implicit. On acquisition of the channel, theadditional APs may send the relative power information to the master AP(e.g., power level feedback).

During an example precoder information stage, the master AP may send theanalog and digital precoder information to the secondary/slave APs. Theanalog precoder may be a full matrix precoder. The analog precoder maybe or include a power adjustment precoder that normalizes the power ofboth APs for power balance.

During an example transmission stage, the APs transmit a JT frame to theSTAs using the analog and digital precoders. These example stages areillustrated in FIG. 21 , FIG. 22 , FIG. 23 and FIG. 24 for explicit andimplicit feedback, where FIG. 21 illustrates an example JT procedurewith master AP for unbalanced power scenario, where the master APdesigns the precoders (explicit feedback).

As shown in FIG. 21 , those processes from 2110 to 2140 represent theexample JT procedure. At 2110, each STA may associate with multiple APsand identify the type of multi-AP transmission it is capable of. Forexample, both APs (e.g., AP1 and AP2) and STAs (e.g., STA1 and STA2)indicate that they are capable of analog and digital processing forpower imbalance. At 2120, powder and channel information may be acquiredby the master AP (e.g. AP1) and AP1 may design precoder through MasterTrigger 2151, NDP 2153, NDP 2154, Master Trigger 2152, FB 2155 and FB2156. Then, AP2 may send the relative power information to AP1, i.e.,Power Level Feedback 2157. At 2130, AP1 may send precoder information toAP2 through Master Trigger 2158, Effective power level Precoder 2159 andMaster Trigger 2160. Then, at 2140, both APs may send a JT frame (i.e.,JT MU-MIMO 2161 and JT MU-MIMO 2162) to the STAs, and the STAs mayreport ACK 2163 and ACK 2164 respectively to the APs.

FIG. 22 illustrates an example JT procedure with master AP forunbalanced power scenario, where each AP designs the precoders (explicitfeedback). As shown in FIG. 22 , those processes from 2210 to 2230represent the example JT procedure. At 2210, each STA may associate withmultiple APs and identify the type of multi-AP transmission it iscapable of. For example, both APs (e.g., AP1 and AP2) and STAs (e.g.,STA1 and STA2) indicate that they are capable of analog and digitalprocessing for power imbalance. At 2220, powder and channel informationmay be acquired by the master AP (e.g. AP1) and each AP may design itsprecoder through Master Trigger 2241, NDP 2242, NDP 2243, Trigger 2244,FB 2245, FB 2246, Power Level Feedback 2247, Trigger 2248, FB 2249, FB2250 and Power Level Feedback 2251. Then, at 2130, AP1 may send MasterTriger 2252 and JT MU-MIMO 2253 to the STAs. AP2 may send JT MU-MIMO2254 to the STAs. The STAs may report ACK 2255 and ACK 2256 respectivelyto the APs.

FIG. 23 illustrates an example JT procedure with master AP forunbalanced power scenario, where the master AP designs the precoders(implicit feedback). At 2310, each STA may associate with multiple APsand identify the type of multi-AP transmission it is capable of. Forexample, both APs (e.g., AP1 and AP2) and STAs (e.g., STA1 and STA2)indicate that they are capable of analog and digital processing forpower imbalance. At 2320, powder and channel information may be acquiredby the master AP (e.g. AP1) and AP1 may design precoder through MasterTrigger 2351, NDP 2353, NDP 2354, Master Trigger 2352, and Power LevelFeedback 2355. Then, at 2330, AP1 may send precoder information to AP2through Master Trigger 2356, Effective power level Precoder 2357 andMaster Trigger 2358. Then, at 2340, both APs may send a JT frame (i.e.,JT MU-MIMO 2359 and JT MU-MIMO 2360) to the STAs, and the STAs mayreport ACK 2361 and ACK 2262 respectively to the APs.

FIG. 24 illustrates an example JT procedure with master AP forunbalanced power scenario, where each AP designs the precoders (implicitfeedback). At 2410, each STA may associate with multiple APs andidentify the type of multi-AP transmission it is capable of. Forexample, both APs (e.g., AP1 and AP2) and STAs (e.g., STA1 and STA2)indicate that they are capable of analog and digital processing forpower imbalance. At 2420, powder and channel information may be acquiredby the master AP (e.g. AP1) and each AP may design its precoder throughMaster Trigger 2441, Trigger 2442, NDP 2443, NDP 2444, Power LevelFeedback 2245, Trigger 2246 and Power Level Feedback 2247. Then, at2430, AP1 may send Master Triger 2448 and JT MU-MIMO 2449 to the STAs.AP2 may send JT MU-MIMO 2450 to the STAs. The STAs may report ACK 2451and ACK 2452 respectively to the APs.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

What is claimed is:
 1. A method of multi-access point (multi-AP)communication performed by a wireless transmit/receive unit (WTRU), themethod comprising: receiving a first trigger frame from a first accesspoint (AP) of a plurality of APs, the first trigger frame comprisingfirst information; receiving a second trigger frame from a second AP ofthe plurality of APs at a predetermined time duration after receivingthe first trigger frame, the second trigger frame also comprising thefirst information of the first trigger frame; generating asynchronization frame based on the first trigger frame and the secondtrigger frame, the synchronization frame comprising synchronizationinformation; transmitting the synchronization frame to at least thefirst AP and the second AP; and receiving a data transmission based onthe synchronization information from each of the first AP and the secondAP.
 2. The method of claim 1, wherein the synchronization informationcomprises transmission power information, transmission starting timeinformation, or transmission frequency information.
 3. The method ofclaim 1, wherein the second trigger frame further comprisesconfiguration information for a second data transmission, wherein theconfiguration information is different from second information of thefirst trigger frame.
 4. The method of claim 3, wherein thesynchronization frame further comprises confirmation informationcorresponding to the configuration information.
 5. The method of claim1, wherein the synchronization frame further comprises third informationof the first trigger frame.
 6. The method of claim 1, furthercomprising: transmitting an ACK/NACK report to each of the first AP andthe second AP.
 7. The method of claim 1, wherein the first trigger framecomprises WTRU-related information.
 8. The method of claim 7, whereinthe WTRU-related information comprises a packet ID, a resourceallocation, a spatial stream allocation, or modulation and coding scheme(MCS) related information.
 9. A wireless transmit/receive unit (WTRU)configured to perform a multi-access point (multi-AP) communication, theWTRU comprising: a receiver configured to receive a first trigger framefrom a first access point (AP) of a plurality of APs, the first triggerframe comprising first information, and a second trigger frame from asecond AP of the plurality of APs at a predetermined time duration afterreceiving the first trigger frame, the second trigger frame alsocomprising the first information of the first trigger frame; a processorconfigured to generate a synchronization frame based on the firsttrigger frame and the second trigger frame, the synchronization framecomprising synchronization information; and a transmitter configured totransmit the synchronization frame to at least the first AP and thesecond AP; wherein the receiver is further configured to receive a datatransmission based on the synchronization information from each of thefirst AP and the second AP.
 10. The WTRU of claim 9, wherein thesynchronization information comprises transmission power information,transmission starting time information, or transmission frequencyinformation.
 11. The WTRU of claim 9, wherein the second trigger framefurther comprises configuration information for a second datatransmission, wherein the configuration information is different fromsecond information of the first trigger frame.
 12. The WTRU of claim 11,wherein the synchronization frame further comprises confirmationinformation corresponding to the configuration information.
 13. The WTRUof claim 9, wherein the synchronization frame further comprises thirdinformation of the first trigger frame.
 14. The WTRU of claim 9, thetransmitter is further configured to transmit an ACK/NACK report to eachof the first AP and the second AP.
 15. The WTRU of claim 9, wherein thefirst trigger frame comprises WTRU-related information.
 16. The WTRU ofclaim 15, wherein the WTRU-related information comprises a packet ID, aresource allocation, a spatial stream allocation, or modulation andcoding scheme (MCS) related information.